The Exciting Star of the Berkeley 59/Cepheus OB4 Complex
and Other Chance Variable Star Discoveries
Daniel J. Majaess1and David G. Turner1
David J. Lane2
Kathleen E. Moncrieff
Department of Astronomy and Physics, Saint Mary’s University, Halifax, NS, B3H 3C3, Canada
1 Visiting Astronomer, Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council of Canada.
2 Abbey Ridge Observatory, Stillwater Lake, NS, Canada.
Accepted for publication in the JAAVSO
Abstract A study is presented regarding the nature of several variable stars sampled during a campaign of photometric monitoring from the Abbey Ridge Observatory: 3 eclipsing binaries, 2 semiregulars, a luminous Be star, and a star of uncertain classification. For one of the eclipsing systems, BD+66°1673, spectroscopic observations reveal it to be an O5 V((f))n star and the probable ionizing star of the Berkeley 59/Cep OB4 complex. An analysis of spectroscopic observations and BV photometry for Berkeley 59 members in conjunction with published observations imply a cluster age of ~2 Myr, a distance of d = 883 ±43 pc, and a reddening of E B–V =1.38 ±0.02. Two of the eclipsing systems are Algol-type, but one appears to be a cataclysmic variable associated with an X-ray source. ALS 10588, a B3 IVn star associated with the Cepheid SV Vul, is of uncertain classification, although consideration is given to it being a slowly pulsating B star. The environmental context of the variables is examined using spectroscopic parallax, 2MASS photometry, and proper motion data, the latter to evaluate the membership of the variable B2 Iabe star HDE 229059 in Berkeley 87, an open cluster that could offer a unique opportunity to constrain empirically the evolutionary lineage of young massive stars. Also presented are our null results for observations of a sample of northern stars listed as Cepheid candidates in the Catalogue of Newly Suspected Variables.
1. Introduction
The present study is the result of a survey of variable stars initiated at the Abbey Ridge Observatory (ARO). Most of the discoveries resulted from the variability of potential reference and check stars in the fields of Cepheid variables, the campaign’s primary objective being to establish period changes for northern hemisphere Cepheids (Turner 1998, Turner et al. 1999). In two cases the interest lies in cluster stars discovered to be variable.
The program began in 1996 at the Burke-Gaffney Observatory (BGO) of Saint Mary’s University, and was recently transferred to the ARO, which is located at a darker site. The stability of the ARO site and an upgrading of the photometric reduction routines facilitated the discoveries, some of which are described here. A preliminary survey was also made of stars in the Catalogue of Newly Suspected Variables (NSV, Samus et al. 2004) thought to be potential Cepheid variables, with the goal of expanding the Galactic sample and eventually studying their period changes. Rate of period change, in conjunction with light amplitude, has been demonstrated to be an invaluable parameter for constraining a Cepheid’s crossing mode and likely location within the instability strip (Turner et al. 2006). Such constraints permit further
deductions to be made concerning a Cepheid’s intrinsic reddening and pulsation mode, and offer yet another diagnostic tool for establishing Cepheids as members of open clusters, such calibrators being the foundation for the extragalactic distance scale (Turner and Burke 2002).
The photometric signatures of some variable stars can be sufficiently ambiguous that spectroscopic follow-up was necessary to resolve the true nature of the light variations. Preliminary results for the best-studied of the variables, summarized in Table 1, are presented here in order of increasing right ascension. The results for the NSV stars are given at the end.
2. Observations and Equipment
The ARO is located in Stillwater Lake, a community ~23 km west of Halifax, Nova Scotia, Canada. The ARO allocates ~2 hours of observing time on each clear night to variable star research, with much of the remainder being used to search for extragalactic supernovae as part of the Puckett Observatory Supernova Search program. The site is quite dark, with typical Sky Quality Meter readings of 20.6 V mag. arcsec–2 on good nights. The observatory houses a 28-cm Celestron Schmidt-Cassegrain telescope equipped with an SBIG ST9-CCD camera and Bessel B and V filters. The facility is remotely accessible and completely automated, allowing unattended acquisition of astronomical and calibration images and providing a software pipeline that calibrates, combines, and performs differential aperture photometry. Much of the design and software development to realize the ARO’s capability was completed in the form of the Abbey Ridge Auto-Pilot software (Lane 2007). Other software, in particular MaxIm DL/CCD (George 2007), provides many of the low-level image acquisition and processing functions.
Observations and image processing are guided by two data files provided by the observer. The first contains relevant information about each field to be imaged, including a unique identifier, center equatorial co-ordinates, and exposure times and number of exposures to be taken in each filter. If aperture photometry is to be performed automatically on the field, additional information is needed, including aperture photometry parameters, magnitude of the designated reference star, and equatorial co-ordinates for each star to be measured. The second file type contains a list of target fields (identifiers) to be observed on a given night.
All resulting photometric data represent means for multiple (15–25, or more) short-exposure images, typically of 1 to 60 seconds duration, taken in immediate succession, combined using a noise-reduction algorithm developed by DJL. The algorithm first calibrates the individual images instrumentally, then registers them spatially using stars in the field. The mean and standard deviation are computed for each pixel position in the stack of images. Pixels on a given image that deviate more than a specified number of standard deviations from the mean of pixels at the same pixel positions on the other images are rejected, and a new mean is computed. The process is iterated up to five times until all deviant pixels are rejected, although no more than 30% of the pixels at a given pixel position are ever rejected. The resulting mean, without inclusion of rejected pixels, is used to form the combined image, which is plate-solved astrometrically using the PinPoint Astrometric Engine software (Denny 2007).
Differential aperture photometry is performed on each combined image using initial aperture and sky annulus parameters, and equatorial co-ordinates of the primary target star, reference star, and any number of “check” or other stars. The sky annulus radius and size are pre-selected for each field to be appropriate for all stars measured. The equatorial position of each star is converted to its corresponding X and Y pixel position using the plate solution embedded in the fts header. Aperture photometry is performed on the reference star 3 times iteratively to
determine its precise X and Y pixel position and full-width half maximum (FWHM) seeing disk.
A new aperture size is set to a pre-determined multiple of the measured FWHM, and the sky annulus position is adjusted so that it remains at the original radius from the star's center. The new aperture parameters and the same technique are used for the remaining stars measured. The instrumental magnitude derived for the reference star is used to convert instrumental magnitudes for the remaining stars into differential magnitudes.
The output for each measured star includes pertinent information, such as FWHM, sky annulus background, signal-to-noise ratio, and maximum pixel value, all of which are invaluable when assessing the data quality. In most instances the reference stars are selected from the comprehensive Tycho-2 catalog (H?g et al. 2000), so there may be zero-point offsets, given that the reference stars are non-standards and the photometry is not explicitly normalized to the Johnson system. Also, differences in color between the reference and target stars are not normally taken into account.
The spectra used to classify the variables were obtained during two observing runs with the Dominion Astrophysical Observatory’s 1.8m Plaskett telescope. During the first run in October 2006, the SITe-2 CCD detector was used to image spectra at a resolution of 120 ? mm–1 centered on 4740 ?. For the second run in October 2007, the SITe-5 CCD detector was used to image spectra at a resolution of 60 ? mm–1 centered on 4200 ?. The spectra were reduced and analyzed using the NOAO’s routines in IRAF along with software packages by Christian Buil (Iris), Valérie Desnoux (Vspec), and Robert H. Nelson (RaVereC). Lastly, a search for periodicity in the photometry of periodic variables in the sample was carried out in the Peranso software environment (Vanmunster 2007) using the algorithms ANOVA (Schwarzenberg-Czerny 1996), FALC (Harris et al. 1989), and CLEANest (Foster 1995).
3. Comments on Individual Stars
3.1 BD+66° 1673 (EA, O5 V((f))n)
BD+66° 1673 lies on the northwestern edge of Berkeley 59, an open cluster embedded in an H II region (Figure 1) at the core of the Cep OB4 association. The star was classified previously from objective-prism spectra as O9-B0 (MacConnell 1968; Walker 1965), but is reclassified as O5 V((f))n from a spectrum at 60 ? mm–1 obtained at the DAO (Figure 2). BD+66° 1673 now has the distinction of being the hottest star in Cep OB4. The star’s implied high temperature drives mass loss via strong stellar winds that may be largely responsible for shaping and illuminating the surrounding H II region, along with playing a role in the formation of clearly-visible, cold, molecular pillars (Yang and Fukui 1992; Gahm et al. 2006).
BD+66° 1673 was monitored as part of a search for variable stars in Berkeley 59, and was the first to exhibit convincing brightness variations. A period analysis of the photometry revealed a strong signal for P = 5.33146 ±0.02000 days. The phased light curve (Figure 3) is that of an Algol-type eclipsing binary system, with primary and secondary eclipse depths of ~0.13 and ~0.06 mag., although with eclipses skewed in phase indicating an eccentric orbit of e? 0.3 and longitude of periastron ω? 180°. Our adopted ephemeris for light minimum in the system from regression fits for the light curve is:
HJD min =2454400.5322 + 5.33146 E.
For the inferred stellar mass and temperature of the primary, a preliminary model generated for the system using Binary Maker 3 (Bradstreet and Steelman 2004) constrains the companion to be an early-to-mid B-type star (B2–B3, say) in a system with an orbital inclination of ~75°. A more detailed photometric study is needed to generate a full light curve to confirm the orbital eccentricity as well as to permit a more detailed analysis.
The distance to BD+66° 1673 can be established from its likely membership in Berkeley 59 and Cep OB4, despite a spatial location outside the cluster nucleus. We obtained all-sky BV photometry of the cluster field on five nights, derived extinction coefficients using the techniques outlined by Henden and Kaitchuck (1998), and standardized the photometry to the Johnson system using stars in the nearby cluster NGC 225 (Hoag et al. 1961). Our data for cluster stars for which we have spectroscopic results are given in Table 2.
BV photometry does not permit one to assess the properties of the dust extinction in the field, and for that we must rely on the UBV photometry obtained by MacConnell (1968) for bright association members. A complete reanalysis is indicated, given that MacConnell (1968) derived different values for the ratio of total to selective extinction (R V) for different stars and regions of Cep OB4. Unusual reddening properties for the dust in the field were first suggested by Blanco and Williams (1959) in their study of Cep OB4. Such properties, if confirmed, would limit the accuracy of any derived distance to the cluster and association stars. We therefore decided to reanalyze the R V estimate from the available photometric and spectroscopic data.
The new spectral classifications for Cep OB4 stars (Figure 2, Table 2) can be used with the UBV photometry of MacConnell (1968) to establish the reddening law for the dust in the field. The result for the four brightest stars is a reddening slope of X = 0.80 ±0.01, identical to the reddening parameters inferred for dust obscuring nearby fields in Cygnus (Turner 1989). The observed UBV colors were dereddened with that reddening law and either zero-age main-sequence (ZAMS) luminosities from Turner (1976a, 1979) or main-sequence luminosities for obvious non-ZAMS stars, with results presented in the variable-extinction diagram of Figure 4. Some stars have colors systematically too blue for their observed spectral types, a feature encountered for many early-type emission-line stars (Schild and Romanishin 1976). The reddening law in Cep OB4 is reasonably well defined by the data, and the slope of the relation depicted in Figure 4 is R V = 2.81 ±0.09 from least squares and non-parametric straight line fits. The slope is consistent with the properties of nearby dust clouds (Turner 1996b).
The distance to Berkeley 59 and Cep OB4 follows from a ZAMS fit, which gives V0–M V = 9.73 ±0.11, corresponding formally to d = 883 ±43 pc. A main-sequence fit to our new photometry for stars in the core of Berkeley 59 (Table 2) is shown in Figure 5 along with data for association members. The results reveal another feature, namely an excess reddening for the B8 III star 2MASS 00021063+6724087: E B–V = 1.5 relative to E B–V = 1.38 ±0.02 for other, spatially-adjacent, cluster members. 2MASS 00021063+6724087 may be an example of a rotating star embedded in a dust torus (see Turner 1996a), and its location in Figure 5 is consistent with a star near the turn-on point for pre-main-sequence objects.
The cluster radial velocity can be deduced by merging observations from Crampton and Fisher (1974) and Liu et al. (1989, 1991), which yields V R = –7 ±15 km s–1 for BD+66° 1674, and –8 ±31 km s–1 for BD+66° 1675. Crampton and Fisher (1974) noted that scatter in the radial velocities for both objects suggested they are spectroscopic binaries. A period search reveals putative periods of P = 1.20 days and P = 5.30 days for BD+66° 1674. The results are sufficiently interesting to justify additional radial velocity measures, which are essential to establish a unique solution.
The presence of a O5 V((f))n star in Berkeley 59 and the predominance of late B-type cluster members lying above the ZAMS indicates an extremely young cluster. An age of ~2 × 106 years for Berkeley 59 is estimated from BD+66° 1673 and the luminosities of stars lying near the cluster turn-on point in Figure 5 (see Guetter and Turner 1997), marking Berkeley 59 as one of the youngest and nearest clusters known. Certainly O5 V((f))n stars are rarely encountered in our Galaxy within a kiloparsec of the Sun. Much like Berkeley 87 discussed later, Berkeley 59 contains a sufficient number of exotic stars to make it an object of intense interest for future studies.
3.2 2MASS 00104558+6127556 (EA, A9 V)
The star 2MASS 00104558+6127556 was found to vary in light during monitoring of the Cepheid BD Cas. A dominant period of P = 2.7172 ±0.0060 days produces a light curve (Figure 3) indicating an Algol-type eclipsing system with eclipse depths of ~0.43 mag. for primary minimum and ~0.31 mag. for secondary minimum. Our adopted ephemeris for light minimum in the system from regression fits for the light curve is:
HJD min =2454404.8586 + 2.7172 E.
A spectrum (Figure 6) indicates a spectral type near A9 V, but with some features that may indicate contamination by a companion. For the inferred stellar mass and temperature of the primary, a preliminary model generated for the system using Binary Maker 3 (Bradstreet and Steelman 2004) constrains the companion to be a mid F-type star (F4-F5, say) in a system with an orbital inclination of ~88°. Additional observations are needed to refine the period and to establish a complete light curve for a formal analysis.
3.3 2MASS 19064659+4401458 (XI?, G2 V)
2MASS 19064659+4401458 lies in the field of the nova-like cataclysmic variable MV Lyr, and was found to display a low level of variability while monitoring the suspected Cepheid NSV 11753 (see section 3.8). The star’s variability was presumably discovered by Weber (1959, number 90 in his list), although it is misidentified in the original finder chart as a different star of constant brightness located a mere 1.4 arcminutes away (NSV 11753, J2000 19:06:54.19, +44:02:55.5). There is X-ray emission at a flux level of 2.21 × 10–2 counts s–1 from within an arcminute of the object (ROSAT ASSC source J190645.9+440139, Voges et al. 2000) that is distinct from an X-ray flux of 1.26 × 10–2 counts s–1 associated with MV Lyr itself (ROSAT ASSC source J190716.8+440109, Voges et al. 1999). The object’s spectral type is G2 V (Figure 6), and its spectroscopic parallax (below) implies an X-ray luminosity of L X? 1030 ergs s–1, as estimated using the energy conversion factor of Huensch et al. (1996). The result is too low for a canonical low-mass X-ray binary (L X≥ 1036 ergs s–1), but is similar to that of W UMa systems (L X ~ 1029-30 ergs s–1, Chen et al. 2006), chromospherically active stars (i.e., RS CVn variables), and compact binaries.
A preliminary period analysis resulted in a dominant signal corresponding to P ? 7.0 days, which is consistent with the initial estimate by Weber (1959) of 8 days, and agrees with more recent estimates by David Boyd and Christopher Lloyd (private communication). The phased light curve in Figure 3 displays a brief eclipse superposed on more rapid, irregular, quasi-
sinusoidal variations. The possibility that 2MASS 19064659+4401458 is a close contact system is inconsistent with the inferred period, and chromospheric activity in the primary is precluded by the absence of Ca II H and K emission in its spectrum.
An alternative scenario would associate irregularities in the light curve with frictional heating in an accretion disk, implying that 2MASS 19064659+4401458 is a semi-detached binary system consisting of a G dwarf overfilling its Roche surface and orbiting a compact companion, presumably a white dwarf. During eclipses the irregular variations disappear, implying that they originate from a hot spot in the accretion disk that is eclipsed by the G2 dwarf. It is hoped that the preliminary results presented here will motivate additional observers to join an ongoing campaign led by variable star observer David Boyd, with a group including Richard Huziak, Roger Pickard, Tomas Gomez, Gary Poyner, Tom Krajci, and Bart Staels, to constrain the period and further investigate the star. An understanding of the system via optical photometry, however, may be limited by the nature of the source driving the irregular variations. Time-series spectroscopy is also needed to assess the full nature of the system.
The object’s distance is estimated from the canonical distance modulus relation reformulated for the infrared, namely with A J = 0.276 × A V and E J–H = 0.33 × E B–V (Bica and Bonatto 2005, Dutra et al. 2002). The 2MASS magnitudes for the star are J = 11.275 ±0.020, H = 10.776 ±0.018, and K = 10.650 ±0.016 (Cutri et al. 2003), and an absolute magnitude and intrinsic color can be established from the star’s main-sequence spectral type as M J = 3.24 ±0.53 and (J–H)0?0.28 ±0.06, parameters deduced from a sample of n? 30 G2 V stars in the Hipparcos database (Perryman et al. 1997) with cited parallax uncertainties ≤0.7 mas. The implied intrinsic color agrees with a value of (J–H)0? 0.38 from Koornneef (1983), when converted to the 2MASS system with the appropriate transformation (Carpenter 2001). The resulting distance for R V = 3.1 is d≈ 310 pc, while, if a nearly negligible field reddening is adopted, as advocated by a 2MASS color-color diagram of the region, it is d≈ 400 pc.
3.4 BD+22° 3792 (SRB, M6 III)
The variability of BD+22° 3792, of spectral type M6 III (Shi and Hu 1999, see Figure 6), was discovered by the ASAS survey (Pojamski et al. 2005). The semi-periodic nature of its photometric variations (Figure 7) and its spectral type are consistent with a Type B semi-regular variable. A Fourier analysis of our observations and those of ASAS-3 implies a possible period around 79 days. The star’s spectral energy distribution displays far-infrared emission, indicating the presence of a warm dusty envelope surrounding the star, likely stemming from mass loss.
BD+22° 3792 is 12′ from the open cluster NGC 6823, but is not a member. The cluster’s associated H II region is excited by numerous, young, reddened, OB stars, which are ~4-7 × 106 years old at a distance of d = 2.1 ±0.1 kpc (Guetter 1992). The star’s distance can be estimated by spectroscopic parallax using photometry taken from Massey et al. (1995) and a set of intrinsic parameters, M V = –0.3 ±0.7 and (B–V)0 = 1.36 ±0.09, derived from a sample of n = 7 nearby M6 giants in the Hipparcos database (Perryman et al. 1997) with cited parallax uncertainties ≤0.9 mas. The intrinsic parameters for M6 giants in the literature are rather scattered (see Mikami 1986, and references therein), mainly because most are variable and exhibit intrinsic color excesses. The resulting distance to BD+22° 3792 is ~700 pc for a reddening of E B–V? 0.38 from the Hipparcos data, while adoption of an intrinsic color of (B–V)0 = 1.58 from Lee (1970) gives d ≈ 950 pc and E B–V? 0.18.
3.5 2MASS 19475544+2722562 (SRB, M4 III)
The star 2MASS 19475544+2722562 lies in the field of the Cepheid S Vul. Its light-curve (Figure 7) exhibits a nearly regular oscillatory trend superimposed upon a gradual increase in brightness. The star’s late spectral type of M4 III (Figure 6) suggests a likely designation as a Type B semiregular. A Fourier analysis suggests a rather short period of ~27 days for the oscillatory trend.
3.6 ALS 10588 = LS II+27 19 (SPB? ELL?, B3 IVn)
Alma Luminous Star 10588 (Reed 1998), or LS II+27 19 (Stock et al. 1960), is a close spatial neighbor of the Cepheid SV Vul, and a likely member of Vul OB1 (Turner 1980, 1984). The star’s evolutionary status from its spectral type (B3 IVn, Figure 6) matches that of stars associated with SV Vul, namely main-sequence objects terminating at B3. Spectroscopic parallax places the star at a distance of 2040 ±470 pc, consistent with the distance to Vul OB1 (d = 2.1–2.5 kpc, Turner 1986; Guetter 1992). ALS 10588 exhibits an IR excess with emission at 60 μm and 100 μm in the IRAS survey (IRAS19498+2717), which might account for its larger space reddening of E B–V = 0.79 ±0.02 relative to a value of E B–V = 0.50 for SV Vul, provided that the former possesses an equatorial dust torus (see Turner 1996a).
The variability of ALS 10588 was revealed during monitoring of SV Vul, although it also appears to have been detected in a VI survey for new Cepheids by Metzger and Schechter (1998).
A period analysis of the photometry revealed a dominant signal at P = 1.8521 ±0.0005 days, although a solution for twice that value (P = 3.704 days) matches our observations and those of ASAS (Pojamski et al. 2005) (Figure 8). The spectral type and period are consistent with the class of slowly pulsating
B stars (SPBs), characterized by stars of spectral types B3–B8 oscillating with periods on the order of days (Waelkens and Rufener 1985). The observed V amplitude (≈ 0.25 mag.), however, is unusually large for a SPB variable (De Cat et al. 2000). Similarly, if twice the period is adopted, the inferred ellipsoidal system has a light amplitude more than twice that observed in other B stars of the same class (Beech 1989). There is also an absence of spectroscopic contamination from the expected companion (Figure 6). A toroidal dust clump orbiting synchronously with the star would account for the IR excess as well as the star’s excess reddening (Turner 1996a), and, if tied to the star’s rotation, would imply a stellar rotational velocity of ~250 km s–1, consistent with the slightly diffuse nature of the star’s spectrum. Yet there is no significant deviation from a repeatable light curve morphology over several seasons of observation. The star’s status may ultimately need to be resolved by time-series spectroscopy to examine whether the resulting radial velocities are consistent with the trend noted for SPBs (De Cat and Aerts 2002), or the canonical features of binarity or extrinsic variability.
3.7 HDE 229059 (α Cyg variable, B2 Iabe)
HDE 229059 is a B2 Iabe supergiant that displays emission in the lower hydrogen Balmer lines (Figure 6) and has an infrared (IR) excess (Clarke et al. 2005). Such characteristics indicate active mass loss and the presence of circumstellar dust. The General Catalogue of Variable Stars (Samus et al. 2004) designates stars with comparable spectral types and V amplitudes (≈ 0.1 mag, Figure 7) to those of HDE 229059 as α Cyg variables, with irregular light variations tied to
overlapping modes of non-radial pulsation. Burki et al. (1978) suggest that all luminosity class Ia B–G supergiants probably vary in brightness (see also Bresolin et al. 2004, and references therein).
HDE 229059 lies in Berkeley 87, an open cluster that has received considerable attention because it is a strong source of γ and cosmic rays (Giovannelli 2002; Aharonian et al. 2006), which has motivated an area of research on how stellar winds interact with the interstellar medium, enabling young open clusters to become pseudo particle accelerators. Berkeley 87 also hosts an abundance of astronomical phenomonae (compact H II regions, molecular clouds, masers, and radio sources) and exotic stellar constituents that includes V439 Cyg, Stephenson 3, and BC Cyg. V439 Cyg is an emission-line star that has exhibited dramatic spectroscopic changes over a short time-scale (Polcaro et al. 1990; Polcaro and Norci 1997; Norci et al. 1998; Polcaro and Norci 1998), Stephenson 3 is a rare type of Wolf-Rayet star (WO3) (Norci et al. 1998; Polcaro et al. 1997), and BC Cyg is an M3 Ia supergiant and type C semiregular variable (Turner et al. 2006) that will eventually terminate in a Type II supernova explosion. The cluster therefore offers intriguing insights into the effects of initial mass and mass loss on the end states of evolution for O-type stars, and may allow us to place new constraints on the initial progenitor masses for WO stars and red supergiants. The situation of HDE 229059 in such an evolutionary scheme is not entirely clear, which is why further study is essential. As a start, we investigate the possibility of cluster membership for the stars using spectroscopic parallax, 2MASS photometry, and proper motion data.
The distance to HDE 229059 can be established by spectroscopic parallax using the photometry of Turner and Forbes (1982) and intrinsic parameters determined from a sample of blue supergiants: M V = –6.4 ±0.8 and (B–V)0 = –0.19 ±0.03 (Kudritski et al. 1999; Blaha and Humphreys 1989; Garmany and Stencel 1992), values that compare favorably with unpublished results (Turner) of M V = –6.3 and (B–V)0 = –0.18 for B2 Iab stars. The distance for R V = 3.0 is d = 970 pc. For BC Cyg, with mean ?V? and ?B–V? from Turner et al. (2006) and intrinsic parameters derived for the comparable M-type supergiant Alpha Orionis, the resulting distance is d≈ 1200 pc.
2MASS photometry (Cutri et al. 2003) for the cluster field yields color-color and color-magnitude diagrams for Berkeley 87 presented in Figure 9. The reddening solution, E J–H = 0.42 ±0.04 (E B–V? 1.36), is well-defined because of the presence of numerous young B-type stars in the cluster. Isochrones for the 2MASS system (Padova Database of Stellar Evolutionary Tracks and Isochrones, Bonatto et al. 2004) fit the data at a distance of d = 1280 ±150 pc. The reddening matches previous results, but the distance is larger than that found by Turner and Forbes (1982), although consistent with a later estimate of 1230 ±40 pc (Turner et al. 2006). Constraining the cluster’s age from 2MASS data is complicated by the fact that BC Cyg lies near the saturation limit of the survey. The isochrone fit in Figure 9 is provided mainly to highlight the envisioned evolution, although high mass loss rates are indicated and the plotted isochrone is more closely linked with conservative mass evolution.
Proper motion data (Zacharias et al. 2004) exist for several bright stars whose membership in Berkeley 87 is supported by their locations in Figure 9, and can be compared with the similar values found for HDE 229059, BC Cyg, and Stephenson 3 (Table 3). The proper motions for such distant stars are small and may be dominated by measuring uncertainties. Consequently, we can only argue that a physical association between the above stars and the cluster cannot be excluded on the available evidence. Membership of the exotic variable stars of Berkeley 87 would be strengthened by radial velocity measures.
3.8 NSV Variables
A number of stars from the Catalogue of Newly Suspected Variable Stars (NSV, Samus et al. 2004) were surveyed in a search for potential small-amplitude Cepheids. Reference stars of well-established magnitude in each field were not available, so the observations were made differentially relative to other stars in the field, with unknown zero-point. The co-ordinates provided by the original sources are estimated to be uncertain by several arcminutes or more, which led us to make photometric sweeps of the immediate field to find objects that might correspond to the suspected variables. There are stars that are reasonably coincident with the co-ordinates for the NSV variables listed in Table 4, but none appear to be light variable. Listed in Table 4 are the co-ordinates from the NSV for the suspected variables, magnitudes from Samus et al. (2004), the standard deviation of the magnitude estimates for the stars selected in the present survey, and the number of observations made. None of the stars identified here in the fields of the suspected Cepheid variables displayed the canonical light variations expected, although other types of variability cannot be dismissed because of our limited observational sampling.
4. Discussion
It is of interest to note how a program of regular observation of Cepheid variables has generated serendipitous discoveries of new variable stars because of the need to establish photometric standard stars and check stars in the fields of the CCD images. In many cases the variable stars prove to be interesting, possibly unique, objects in their own right. But additional photometric and spectroscopic observations may be essential for clarifying their overall properties.
We are indebted to the following groups for facilitating the research described here: the staff at la Centre de Données astronomiques de Strasbourg, 2MASS, and NASA’s Astrophysics Data System (ADS). We are particularly grateful to Conny Aerts for relevant discussions on SPBs, David Boyd and Christopher Lloyd for sharing their insights on 2MASS 19064659+4401458, Robert H. Nelson for sharing his expertise in various areas, and Dmitry Monin, Les Saddelmeyer, and the rest of the staff at the Dominion Astrophysical Observatory.
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Table 1. Monitored variable stars
Star RA(2000) DEC(2000) Type P (days) Sp. Type
BD+66° 1673 00:01:46.86 +67:30:25.1 EB 5.33146 O5 V((f))n
2MASS 00104558+6127556 00:10:45.58 +61:27:55.6 EB 2.7172 A9 V
2MASS 19064659+4401458 19:06:46.82 +44:01:46.5 XI? 7.0: G2 V
BD+22° 3792 19:43:53.00 +23:11:36.0 SRB 79.4: M6 III
2MASS 19475544+2722562 19:47:55.52 +27:22:57.8 SRB 27.3: M4 III
ALS 10588 19:51:52.87 +27:25:00.1 SPB? 1.8521 B3 IVn
… … ELL? 3.704 …
HDE 229059 20:21:15.45 +37:24:35.2 α Cyg … B2 Iabe
Table 2. Photometry and spectroscopy of Berkeley 59 members
Type Star MacC1 RA(2000) DEC(2000) V B–V Sp.
BD+66° 1673 3 00:01:46.91 +67:30:24.3 10.07±0.04 1.31±0.03 O5 V((f))n
BD+66° 1675 14 00:02:10.32 +67:24:32.5 9.08±0.03 1.08±0.02 O7 V
BD+66° 1674 13 00:02:10.68 +67:25:44.5 9.60±0.04 1.07±0.02 B0 IIIn
MacConnell 15 15 00:02:13.42 +67:25:05.5 11.30±0.03 1.08±0.02 B0.5 Vn
2MASS 00020012+6725109 A3 00:02:00.17 +67:25:11.2 12.81±0.03 1.20±0.01 B3 V
2MASS 00021063+6724087 … 00:02:10.63 +67:24:08.7 13.43±0.02 1.36±0.03 B8 III
Note: 1 Numbering from MacConnell (1968).
Table 3. Proper motion data for Berkeley 87 stars.
2
RA DEC
3 HDE 229059 –4.5 ±0.6 –5.3 ±0.7
4 … –5.2 ±0.7 –5.
5 ±1.0
13 … –5.6 ±0.7 –7.5 ±0.7
15 V439 Cyg +1.1 ±5.4 +11.2 ±5.4
25 … –3.9 ±0.7 –5.7 ±1.1
26 … –5.7 ±1.3 –4.1 ±2.4
29 Stephenson 3 –8.0 ±5.4 –2.8 ±5.4
32 … –5.1 ±2.0 –3.1 ±0.7
78 BC Cyg –4.5 ±1.1 –7.7 ±1.1 Note: 2 Numbering from Turner and Forbes (1982).
Table 4. Cepheid Candidates from the NSV Catalogue.
3
NSV 00924 02:48:19.91 +58:41:44.8 12.50 ±0.003 3 NSV 11753 19:06:54.19 +44:02:55.5 13.50 ±0.007 16
NSV 11931 19:21:11.73 +00:07:02.6 14.20 ±0.014 7 NSV 14094 22:16:16.71 +49:13:13.8 12.10 ±0.008 8 NSV 14237 22:35:04.02 +63:47:37.6 12.30 ±0.006 8 Note: 3 From Samus et al. (2004).
Figure 1. The field of view of Berkeley 59, a pseudo color image constructed from POSS II data.
Figure 2. A mosaic of continuum-normalized CCD spectra for likely members of Berkeley 59 and Cep OB4.
19064659+4401458.
Figure 4. A variable-extinction diagram for likely main-sequence and zero-age main-sequence (ZAMS) members of Berkeley 59 and the Cep OB4 association. Least squares and non-parametric fits yield a ratio of the total to selective
extinction of R V = 2.81 ±0.09.
Figure 5. A reddening-free BV color-magnitude diagram for Berkeley 59 (open circles) and Cep OB4 (filled circles).
A ZAMS fit to the observations yields a distance of d = 883 ±43 pc and a reddening of E B–V = 1.38 ±0.02 in the core
of the cluster.
Figure 6. A mosaic of CCD spectra from the DAO 1.8-m Plaskett telescope for variables examined in this study.
Figure 7. Light curves for variables examined in this study, constructed from differential photometry from the ARO. Zero-point offsets are expected (see text), although the standard deviation of observations for check stars in the same
fields ranges from ±0.006 to ±0.008 mag.
days.
Figure 9. A color-color diagram (lower) and color-magnitude diagram (upper) for Berkeley 87 constructed from 2MASS data. The intrinsic color-color relation for the 2MASS system (Turner unpublished) is depicted as a solid line, as well as reddened by E J–H = 0.42 ±0.04 (E B–V? 1.36) as a dotted line (lower). Filled circles correspond to stars likely to be cluster members. An isochrone fit (upper) is provided to highlight the assumed evolution (see text). The variable stars HDE 229059 (J = 5.551) and BC Cyg (J = 2.117) are provided with photometric error bars (BC Cyg is
near saturation).
1. 由于是浙江选考生，在高中第一次选考中化学只取得了91分的成绩，只剩下一次选考机会，成绩说好不算好，说坏不算坏的情况下，提升有些困难。不知道该放弃还是继续参加考试。如果不能达到97或100的成绩，可能会被目标大学相同的同学在高考上拉开差距。晚上也睡不好觉，经过一段时间的调整心态，说服自己还是奋力一搏。于是到选考前我每天利用下课时间翻看化学书和整理笔记，努力记住容易混淆的基础知识点，每天晚自习刷一张化学模拟卷，自批订正纠错，找到了自己很多弱点和盲点，并针对的做专题练习。终于在四月选考中达到了97的目标。虽然很累，但是为了实现离考上理想大学的目标更进一步，还是值得的。 专业知识技能——基础化学知识 可迁移技能——记忆、纠错（找到自己的弱点）、反省、整理、权衡利弊 自我管理技能——自我控制、抗压、调整心态、坚持不懈 2. 上个学期选专业时想要进入生物科学专业，但是看到报名的人数有点多，招收人数与报名人数之比大约是1/2，要经过面试淘汰一部分人。而且在看到身边的同学都非常优秀的情况下，竞争压力有些大，我心中也有些底气不足。但我还是迫使自己鼓起勇气报了名。报名之后，我上网了解记住了一些生物科学的知识，回忆了我高中时期学习生物的一些知识和经历，找到一些我可能在面试中能够用到的素材。并在脑海中模拟了几个面试中可能会提到的问题，并想了想如何回答。此外也找到我们寝室作为生命科学学院教授的新生之友询问了一些情况。到了面试那天，我准备的其中一些素材和回答派上了用场，顺利地应对面试教授提出的问题，通过了面试，成功进入生物科学专业，提升了我的信心。 专业知识技能——生物科学部分知识 可迁移技能——记忆、模拟（假想）、询问求助、面试交流、做好充分准备 自我管理技能——鼓起勇气（自我调节心态）、有信心的、自我控制 3. 小时候老师说我钢笔字写的挺好的，在小学的钢笔字比赛中获了奖，我可能
电磁耦合原理及公式 悬赏分：0 - 解决时间：2006-9-10 21:41 定子与转子如何产生感应电压 提问者：jinshoufeng - 一级 最佳答案 磁铁和电流都能够产生磁场，电流的磁场是由电荷的运动形成的，那么磁铁的磁场是如何产生的呢？法国学者安培根据环形电流的磁性与磁铁相似，提出了著名的分子电流的假说。他认为，在原子、分子等物质微粒内部，存在着一种环形电流——分子电流，分子电流使每个物质微粒都成为一个微小的磁体，它的两侧相当于两个磁极。这两个磁极跟分子电流不可分割地联系在一起。安培的假说，能够解释各种磁现象。一根软铁棒，在未被磁化的时候，内部各分子电流的取向是杂乱无章的，它们的磁场互相抵消，对外界不显磁性。当软铁棒受到外界磁场的作用时，各分子电流的取向变得大致相同，软铁棒就被磁化了，两端对外界显示出较强的磁作用，形成磁极。磁体受到高温或者受到猛烈的敲击会失去磁性，这是因为在激烈的热运动或机械运动的影响下，分子电流的取向又变得杂乱了。在安培所处的时代，人们对原子结构还毫无所知，因而，对物质微粒内部为什么会有电流是不清楚的。直到20世纪初期，人类了解了原子内部的结构，才知道分子电流是由原子内部的电子的运动形成的。安培的磁性起源的假说，揭示了磁现象的电本质。它使我们认识到，磁铁的磁场和电流的磁场一样，都是由电荷的运动产生的。 但是仅凭“电荷运动产生磁场”还不足以说明以下三个问题：1.运动电荷周围的磁场为何其磁力线方向符合右手螺旋法则而不是左手螺旋法则？2.通电直导线周围有环形磁场，为何磁力线方向也符合右手螺旋法则而不是左手螺旋法则？3.原子磁矩如何确定N极和S极？唯一的解释只能是“电荷运动时自旋”，自旋产生磁场，磁力线方向与自旋方向有关。“电荷运动时自旋”这一判断虽然是来自于推理，但能够解释一切电磁现象，下面一一讲述： 一、电生磁 电荷静止时不自旋，只产生电场，不产生磁场。 电荷运动时自旋，并在周围产生环形磁场。正电荷运动时的自旋方向和磁场方向为：右手半握，拇指伸开，拇指指向正电荷前进方向，其余四指就指向自旋方向，磁力线方向与自旋方向相同。负电荷运动时的自旋方向和磁场方向为：左手半握，拇指伸开，拇指指向负电荷前进方向，其余四指就指向自旋方向。磁力线方向与自旋方向相反。 通有直流电流的直导线中，电子排着队向前运动，因电子自旋的作用，导线周围有环形磁场。电子自旋方向和磁场方向为：左手半握，拇指伸开，拇指指向负电荷前进方向，其余四指就指向自旋方向，磁力线方向与自旋方向相反。 若将通有直流电流的直导线弯曲成圆形，则环形磁场闭合，对外表现为磁矩。电流方向和磁极方向的关系符合右手螺旋法则：右手半握，拇指伸开，除拇指外的四指指向电流方向，则拇指指向N极方向。 电子绕原子核运动，可视为通有直流电流的圆形导线，对外表现为原子磁矩。电子运动方向和磁极方向的关系符合左手螺旋法则：左手半握，拇指伸开，除拇指外的四指指向电子运动方向，则拇指指向N极方向。 二、电作用于磁
S T A R法成就故事
1、由于家里比较贫穷，因此大学以前就没有接触过电脑，第一节上计算机文化基础时，一点也不明白，年轻人难免有好胜之心，因此我认真学习课本，遇到不懂的问题及时向同学及老师请教，由于考试考word等办公软件，因此我上网浏览资料，下载了office教程，一有时间就去机房实践，不明白就请教机房老师，经过许多次的练习，我终于掌握了计算机基础知识，通过了考试。 这个故事中，琢磨、实践是可迁移技能，word等软件知识是专业知识技能，认真是自我管理技能。 2、大一的时候，我没有拿到奖学金，看到有的同学拿到奖学金后的兴奋，我心里暗暗下定决心要在大二拿到奖学金。为了实现这个目标，我付出了许多。上课时认真听讲，做好课堂笔记，课下认真做好老师布置的作业，有不懂的问题及时向老师和同学请教，考前做好复习。经过一年的努力，获得了染整专业知识，并且在大二成功获得了奖学金。 这个故事中，认真是自我管理技能，请教、获得是可迁移技能，染整知识是专业技能。 3、大学寒假春节我在超市当售货员。我主要销售零食。一方面加强了有关销售零食知识的学习，虚心向其他店员请教。一方面了解实际情况，在短时期适应下来。及时上岗工作走上正轨，负起了超市店员的职责。工作几周后对商品的规划与陈列有了了解，感受到市场的学问与超市零售的知识是如此的深广。在期间发生过意外但通过冷静的自省，认识自己的不足，整体上因参与营运时间较短，操作不够自如外，这是由于经验少。经过超市员工的共同的努力，我们
的销售有了明显的增长。而我在严格要求的基础之上，发现问题，消减漏洞，作一名称职的超市店员。 这个故事中，严格、虚心是自我管理技能，适应、发现、请教是可迁移技能，销售零食知识是专业技能。 4、我学会了使用CAD软件。这学期我们学习了AUTO CAD 课程，我真切地体 会到了这种绘图系统的实用性。首先熟悉用户界面,学习新建图形、绘制简单图形的操作。掌握坐标及数据的输入方法，绘出下面所示图形，打开工具栏的方法，打开“对象捕捉”工具栏。同时学会利用栅格绘制图形。设定CAD图形界限的方法，掌握绘制CAD图形的基本绘图命令熟练运用对象捕捉定点工具，精确绘制图形熟悉圆、圆弧、椭圆、点等画法掌握CAD各种图形编辑命令，如镜像、偏移、阵列等的用法和功能了解选择图形对象的多种方法掌握设定图层的方法养成按照图层绘制不同属性对象的画图习惯。在今后的学习工作中，好好利用CAD，再接再厉，更加努力的学习，希望在以后的学习中能够熟练掌握这门技术。 这个故事中，熟悉、学会、利用是可迁移技能，CAD知识是专业知识技能，努力、熟练是自我管理技能。 5、上大学以来，一直就想找个机会锻炼一下自己，在大二暑假我去了浙江向胜体育器材厂做社会实践。在工作中，我对机械的自动化有了更深的了解，对工作中出现的问题，我也及时地向老师傅请教，很快就学会了机器的操作方法，由于车间条件恶劣，养成了吃苦耐劳的精神，看着生产线上我做的零件，我感觉特别有成就感。 这个故事中，请教是可迁移技能，吃苦耐劳是自我管理技能，机器操作方法是专业知识技能。
STAR法则,即为Situation Task Action Result的缩写，具体含义是: Situation: 事情是在什么情况下发生 Task: 你是如何明确你的任务的 Action: 针对这样的情况分析，你采用了什么行动方式 Result: 结果怎样，在这样的情况下你学习到了什么 简而言之，STAR法则，就是一种讲述自己故事的方式，或者说，是一个清晰、条理的作文模板。不管是什么，合理熟练运用此法则，可以轻松的对面试官描述事物的逻辑方式，表现出自己分析阐述问题的清晰性、条理性和逻辑性。 详细释义 STAR法则,500强面试题回答时的技巧法则,备受面试者成功者和500强HR的推崇（宝洁HR培训资料有专门的讲座讨论如何用此法则检验面试者过往事迹从而判断其能力）。 如果对面试技巧和人力资源招聘理论有所了解的同学应该听说过,没听说也无所谓,现在知道也不迟。由于这个法则被广泛应用于面试问题的回答，尽管我们还在写简历阶段，但是，写简历时能把面试的问题就想好，会使自己更加主动和自信，做到简历，面试关联性，逻辑性强，不至于在一个月后去面试，却把简历里的东西都忘掉了（更何况有些朋友会稍微夸大简历内容） 在我们写简历时，每个人都要写上自己的工作经历，活动经历，想必每一个同学，都会起码花上半天甚至更长的时间去搜寻脑海里所有有关的经历，争取找出最好的东西写在简历上。 但是此时，我们要注意了，简历上的任何一个信息点都有可能成为日后面试时的重点提问对象，所以说，不能只管写上让自己感觉最牛的经历就完事了，要想到今后，在面试中，你所写的经历万一被面试官问到，你真的能回答得流利，顺畅，且能通过这段经历，证明自己正是适合这个职位的人吗？ 编辑本段 示例 写简历时就要准备好面试时的个人故事，以便应付各种千奇百怪的开放性问题。 为了使大家轻松应对这一切，我向大家推荐“个人事件模块”的方法，以使自己迅速完成这看似庞大的工程。 一，头脑风暴＋STAR法则——〉个人事件模块 1．1，头脑风暴。 在脑海里仔细想出从大一到大四自己参与过所有活动（尤其是能突出你某些能力的活动），包括： 1，社团活动职务时间所做事情 2，在公司实习的经历职务时间所做过的事情 3，与他人一起合作的经历（课题调研，帮助朋友办事） （回忆要尽量的详细，按时间倒序写在纸上，如大一上学期发生。。。。。。大一下学期发生。。。。。。。如此类推） 我相信这一步，很多朋友都已经做了，但是仅仅这样就满足了，就直接写在简历上当完事了，那是不行的，想提高竞争力，还得继续。。 1．2，STAR法则应用 将每件事用S T A R 四点写出，将重要的事情做成表格 例大一辩论比赛获得冠军 S 系里共有5支队伍参赛，实力。。。，我们小组。。。。。
学科前沿讲座作业 ——隧道及地下结构性能与环境耦合作用机制本次的土木工程前沿讲座主要是由丁祖德老师为我们讲解，关于隧道及地下结构性能的知识。此次课程包含有三个主题，主题之一：高速铁路隧道基底软岩动力特性及结构安全性研究（疲劳问题）；主题之二：硫酸盐侵蚀环境下隧道结构损伤机制及演化规律（腐蚀问题）；主题之三：地下结构性能与环境耦合作用机制（全寿命：疲劳+腐蚀+其他）。虽然我们不是学的这个方向，但是为了丰富我们的知识体系，拓展我们的知识框架，这个讲座还是非常有意义的。 针对主题一的内容主要讲解了：混凝土和软岩弹塑性损伤模型，隧道基底软岩动变形特性试验，高速铁路隧道底部基岩动力响应特性分析，高速铁路隧道地基长期累积变形分析，基底状况对高速铁路隧道结构性能的影响。 随着改革开放的推移，中国经济飞速发展，为了满足社需需要，高铁就成为发展的一个推动因素，然而高铁的速度快，需要的工艺，施工，技术的要求就更高，稳定性也成为其研究的方向。高速铁路建设由于要求高，结合我们的国家地理位置情况，势必会涉及到大量隧道的开挖。高铁所处的地理位置不同，地下的地质条件也不同，在软弱段会出现沉降问题，这对高铁是一个致命性的问题，需要研究处理，以保证铁路的正常运行，这对隧道的结构动力稳定性要求则更高。隧道还存在一定的结构病害，例如结构开裂、破损、下陷等病害。这些多需要研究处理，以达到设计及运行要求，保证工程的质量，符合社
会需求。在这些研究中会涉及到的主要因素及意义有：隧道衬砌结构和基底围岩的动力损伤量，高速铁路隧道地基长期累积变形，基底状况对高速铁路隧道结构性能的影响，我国高速铁路隧道的合理设计和施工提供科学依据。 研究现状 当列车在不平顺轨道上行驶时，轮轨间相互作用力将会通过轨道系统传递到隧道支护结构上，激起隧道支护结构的振动，从而影响结构的耐久性和使用寿命；同时，随着振动在地层中的传播与扩散，进一步对周边环境产生影响。隧道列车振动响应问题涉及振源、隧道结构和地层的振动响应以及振动响应环境影响等方面。针对列车荷载作用下隧道结构动力响应问题，国内外学者进行了大量研究，但这些研究大多针对的隧道结构本身，对隧道周边围岩动力响应问题研究不多。而对于动力作用下的地层累计变形研究方面，目前主要集中在路基变形研究。早在1955年，有人根据黏土循环三轴试验，提出动应力水平越高，累计变形越大。其后，许多学者基于理论和实验研究，分析加载次数，动应力和围压比值等对土体累计变形影响，但对于列车往复动载作用下隧道基层砂层累计变形研究还是太少。而在丁老师讲解的过程中，还是有这方面的研究。 隧道振动与诸多因素相关，其分析涉及列车、隧道结构、土层的模拟以及相互作用，各分部动力参数的确定以及远、近动力特性的描述。由于解析计算的局限性，采用数值计算方法进行隧道振动响应分析已获得越来越多的认可，逐渐成为隧道列车振动响应分析的主要手
第一章单元测试 ?名称大学生就业与创业指导 ?对应章节第一章 ?成绩类型分数制 ?截止时间 2017-12-01 23:59 ?题目数5 ?总分数 100 ?说明: ?评语: ?提示：选择题选项顺序为随机排列，若要核对答案，请以选项内容为准100 ?第1部分 ?总题数:5 ? 1 【多选题】(20分) 关于职业发展模型，以下描述正确的是：（） A. 职业选择或定位时，自我方面主要考虑能力与需求，职业方面要了解要求与回馈。 B. 当个人的能力符合职业的要求时，组织对个人较满意。 C. 当职业的回馈满足个人的需求时，个人对组织较满意。 D. 任何职业选择要同时考虑组织满意度与职业满意度两个维度。 正确 查看答案解析 ? ?本题总得分：20分 2 【多选题】(20分)
职业对技能的要求通常可分为三种类别，分别是：( ) A. 知识技能 B. 可迁移技能 C. 管理技能 D. 自我管理技能 正确 查看答案解析 ? ?本题总得分：20分 3 【多选题】(20分) STAR成就故事深度分析法，是有效分析个人能力的方式。对“STAR”原则描述正确的是：（） A. Situation情境——当时面对什么困难？ B. Target目标——你的目标是什么？ C. Action行动——你做了什么？ D. Result结果——效果如何？你有什么收获？ 正确 查看答案解析 ? ?本题总得分：20分 4 【多选题】(20分)
参加大型招聘会时，应注意：（） A. 最好提前通过招聘会网络发布的信息了解企业和岗位 B. 带一个版本的简历即可，看到中意的企业就投递 C. 要有针对性地投递简历，主动提问交流 D. 及时记录投递简历情况、公司名称、应聘岗位、联系人等。 正确 查看答案解析 ? ?本题总得分：20分 5 【多选题】(20分) 获取就业信息的渠道有：（） A. 网络 B. 招聘会 C. 实习实践 D. 人际资源 E. 直接与用人单位联系 正确 第二章单元测试 ?名称大学生就业与创业指导
激光-光纤耦合效率测量数据处理与分析1、数据处理与分析 分析：由表1 激光-光纤耦合效率测量数据表可知，实验所测得的单模光纤耦合效率约为22.27%；而多模光纤耦合效率约为 70.68%；很明显，多模光纤耦合效率远远高于单模光纤的耦合 效率。 2、误差分析 本实验误差较大，主要来自于以下几方面： （1）激光器、显微镜以及光纤不可能百分百的准直，一定会存在微小的偏差，这会对实验结果产生一定的误差。 （2）光源并没有接触光纤，也就是说光需要在空气中传输一小段距离才能进入光纤，这会有一定的衰减，这也会造成一定的误差。 （3）由于光纤具有衰减因素，所以光在光纤中传输也会有一定的衰减，导致所测得的进入光纤的光功率偏小，从而导致耦合效率偏
低。 （4）另外，光纤接口，以及弯曲都会影响光纤的耦合效率，从而导致实验误差。实验中注意到用手稍微抬着光纤接口附近一点，以及尽量使光纤直，会使光功率变大，这说明光纤弯曲也会导致实验误差，使实验所测得的耦合效率偏小。 3、实验总结 通过此次实验，我明白了光纤与光源耦合方法的原理及提高耦合效率的措施；对激光器输出光强度的分布有了深入地学习和了解；对光纤的模式及基模光强度的分布有了新的认识。同时也学会了如何测量光纤与光源的耦合效率，知道了影响光纤与光源耦合效率的因素以及如何提高光纤耦合效率。 4、思考题 （1）分析提高耦合效率的关键途径。 答：①使用多模光纤进行传输；②使用透镜对光源进行聚焦后再送入光纤；③增大光纤数值孔径；④使用发射面极小的激光光源； ⑤在耦合处尽量使光纤准直。 （2）实验中是否可以更换其它的聚焦透镜，有何依据? 答：实验中不可以更换其它聚焦透镜。原因有二，其一，为了最有效地把光入射到光纤中去，通常应采用其数值孔径与光纤数值孔径相同的透镜进行聚光，如果更换就会影响激光与光纤的耦合效率，从
光电耦合隔离端子的原理和作用 信号隔离的目的之一是从电路上把干扰源和易干扰的部分隔离开来，使测控装置与现场仅保持信号的联系，但不直接发生电联系。随着自动化程度的不断提高，控制和现场电路之间的隔离日益显示出重要性，作为自控系统的核心，控制单元必须与各传感器和执行器可靠地隔离开来，以避免干扰。 光电耦合隔离端子 电路中为什么要使用光耦器件？ 电气隔离的要求。A与B电路之间，要进行信号的传输，但两电路之间由于供电级别过于悬殊，一路为数百伏，另一路为仅为几伏；两种差异巨大的供电系统，无法将电源共用； A电路与强电有联系，人体接触有触电危险，需予以隔离。而B线路板为人体经常接触的部分，也不应该将危险高电压混入到一起。两者之间，既要完成信号传输，又必须进行电气隔离； 运放电路等高阻抗型器件的采用，和电路对模拟的微弱的电压信号的传输，使得对电路的抗干扰处理成为一件比较麻烦的事情——从各个途径混入的噪声干扰，有可能反客为主，将有用信号“淹没”掉； 除了考虑人体接触的安全，又必须考虑到电路器件的安全，当光电耦合器件输入侧受到强电压（场）冲击损坏时，因光耦的隔离作用，输出侧电路却能安全无恙。 以上四个方面的原因，促成了光耦器件的研制、开发和实际应用。光耦的基本作用，是将输入、输出侧电路进行有效的电气上的隔离；能以光形式传输信号；有较好的抗干扰效果；输出侧电路能在一定程度上得以避免强电压的引入和冲击。 上海联捷电气利用现有的轨道式接线端子连接技术,并加装了电子元器件组成的电路,实现了光电过程的传输耦合。光隔端子具有控制端信号损耗小、切换频率高、无机械触点抖动、无磨损切换、绝缘电压高、不怕振动、不受位置影响且寿命长等优点，因此在自动控制领域得到了广泛应用。
共射基本放大器的功率和效率 刁修睦 （潍坊学院 信息与控制工程学院，山东 潍坊 261061） E-mail:ddxxmm_001@https://www.doczj.com/doc/ec12550352.html, 摘 要：本文以共发射极基本放大器为例，对低频小信号电压放大器的输出功率和转化效率作了定量讨论，给出了在理想状态下的该电路输出功率和转化效率的定量计算公式，说明了该电路效率太低的原因及提高效率的方法。 关键词： 不失真输出功率；效率；尽限运用；阻抗匹配 模拟电子技术以放大器为主要研究对象，基本放大器是一切放大电路的基础，明确基本放大器优缺点，并找出提高其性能的措施，对增强整个教学过程的系统性至关重要。一般教材均侧重于对基本放大器的放大能力及输入、输出电阻的讨论，而对其功率及转化效率不予讲述。本文以共发射极基本放大器为例，对低频小信号电压放大器的输出功率和转化效率作了定量讨论，给出了在理想状态下该电路的输出功率和转化效率的定量计算公式，说明了该电路效率太低的原因及提高其效率的主要方法。通过讨论，进一步明确了放大器放大的实质，并可自然引出有关功率放大器的相关内容，使教材的系统性进一步加强，收到较好的教学效果。 一、电路及特性方程 共发射极基本放大器是最常用的小信号电压放大器之一。图一（a ）是阻容耦合共射基本放大器的原理图；图一（b ）是其交流通路；图二是由图解法得出的与该电路对应的直流负载线、最佳交流负载线及最大不失真输出信号的波形。假设所有元件均为理想元件。本文依据该电路及相应波形推导出放大器的输出功率和转化效率的数学表达式。为此，首先明确各相关量之间的关系。 (a) (b) R L 图一 共射基本放大电路
由图一(a)得该电路的直流负载方程为： V CE =E C -I C ?R C ----------------------------------------------------------------------- (1) 对应于不失真的放大的最佳工作点Q ，有： V CEQ =E C -I CQ ------------------------------------------------------------------------ (2) 由图二可得其相应的交流负载方程为： V CE = E C ′- i C ?R L ′-----------------------------------------------------------------------(3) 以上各式中，V CE 为C 、E 极间的静态电压，V CEQ 为其最佳静态工作电压，V CE 为其动态瞬时电压；E C 为直流电源电压，E C ′为动态等效电源电压；I C 为静态集电极电流，I CQ 为最佳静态集电极电流，i C 为动态瞬时集电极电流；R L 为集电极负载电阻，R L ′为放大器交流通路的等效负载电阻（R L ′=R L // R C ）。 当静态工作点Q 选在最佳点时，且在忽略晶体管的饱和压降和截止区的一段压降的条件下，将Q 点选在教流负载线的中点。由图二可知： E C ′= 2V CEQ ---------------------------------------------------------------------------------- (4) 且 V CEQ = I CQ ? R L ′------------------------------------------------------------------------------- (5) 将(4)代入(3)得： V CE =2 V CEQ - i C ?R L ′ ------------------------------------------------------- (6) 将(5)代入(2)并整理得： CE (V) I CQ 图二 共射放大电路输出波形
收稿日期：2017-03-31 基金项目：国家自然科学基金资助项目（51675155）0引言无损检测技术在不损伤被检测对象的条件下，利用材料因内部结构异常或存在缺陷而引起的对热、声、光、电、磁等反应的变化，来探测其表面或内部缺陷［1］。金属磁记忆技术（MMM ）作为磁性无损检测的一种［2］，能够对铁磁性材料的微裂纹和早期损伤进行检测和评估，得到了研究人员的广泛关注［3］。金属磁记忆的原理是对自发漏磁场进行分析， 而这种自发漏磁场是由材料的应力集中、组织结 构不完整和不均匀引起的［4］，主要物理效应为磁机 械效应和磁弹性效应［5］。金属磁记忆实质上是一 种在地磁场激励作用下的力磁耦合效应，采集到 的是一种弱磁信号，因此它易受到铁磁材料本身 的化学成分、试件尺寸、缺口形状、表面处理工艺和 环境磁场等多种因素的干扰［6］。文献［7］的研究 表明，磁记忆试验得到不同结果的原因可能是弱 磁信号极易受到环境磁场的干扰。文献［8-10］激励磁场对力磁耦合作用的强化机制研究 刘志峰费志洋黄海鸿钱正春 合肥工业大学绿色设计与制造工程研究所，合肥，230009 摘要：力磁耦合作用是金属磁记忆检测等电磁无损检测技术的基础。为了探明外加激励磁场在不同应力水平下对力磁耦合作用的影响机制，从磁导率与应力及环境磁场变化关系的角度，在理论上计算了外加激励磁场下力磁耦合作用下与力和磁单独作用下的表面磁场强度之差ΔH ，并推导出该差值随着拉应力的增大而增大的结论。用预制缺陷的45钢试样进行对照试验，发现激励磁场对力磁耦合作用的影响ΔH 是随着应力的增大而呈类似指数形式递增的。经设计的正交试验验证，激励磁场与应力对磁信号的交互耦合作用显著，且在受力过程中激励磁场对信号的作用水平最大，这与理论分析结果吻合。说明外加激励磁场对力磁耦合作用起到了一定的强化作用。 关键词：激励磁场；力磁耦合；强化；金属磁记忆 中图分类号：TG115.28 DOI ：10.3969/j.issn.1004-132X.2018.09.015开放科学（资源服务）标识码（OSID ）： Study on Strengthening Mechanism of Excitation Magnetic Field to Stress -magnetization Coupling Effects LIU Zhifeng FEI Zhiyang HUANG Haihong QIAN Zhengchun Institute of Green Design and Manufacturing Engineering ，Hefei University of Technology ，Hefei ，230009Abstract ：The stress -magnetization coupling effect was the basis of metal magnetic memory detection and other electromagnetic nondestructive testing technology.To investigate the mechanism of the excitation magnetic field to stress -magnetization coupling effect under different stress levels ，a differential value ΔH ，was calculated theoretically from the relationship of permeability and stress and environmental magnetic field ，which was the difference between the magnetic field strength affected by stress or magnetism interactively and by them individually.It was deduced that ΔH increased with the increases of tensile stresses.A control test was conducted with a prefabricated defective 45steel sample ，and it is found that ΔH ，characterized the effects of the excitation magnetic field on the stress -magnetization coupling ，increases exponentially with the increases of the stresses.And the orthogonal experiment was designed to verify that the interactions between the excitation magnetic field and the stress on the magnetic signals were significant.In the loading processes ，the excitation magnetic fields were the greatest impacts on the signals.These are consistent with the theoretical analyses.The results show that excitation magnetic field plays a certain role in strengthening the stress -magnetization coupling effects. Key words ：excitation magnetic field ；stress -magnetization coupling ；strengthening ；metal magnetic memory ··1108万方数据
什么是光电耦合器?其原理作用是什么 光电产品是我们现代生活中必不可少的一种设备，它为我们的生活带来了诸多的便利。光电产品能够正常的使用，是离不开光电器件的。光电耦合器就是这样一种非常重要的光电器件。但是，小编相信绝大多数读者朋友都不是很了解光电耦合器的原理和作用，下面小编就为大家详细介绍光电耦合器的相关知识，希望带领大家了解这种器件的原理和作用。 光电耦合器简介 什么是光电耦合器呢?它是一种以光为主要媒介的光电转换元件，它能够实现由光到电、再由电到光的转化。光电耦合器又叫光电隔离器。它能够对电路中的电信号产生很好的隔离作用，特别是在照明的电路中，它更是能够有效地保护电路和导线，使光信号和电信号互不干扰，各自进行工作，确保了电源和光源各自的正常有序工作，具有较好的电绝缘能力和防干扰能力。生活中常见的光电耦合器有很多种类，如光电二极管、三极管，光敏电阻、光控型晶闸管，这些都属于很不错的光电耦合器。 光电耦合器原理 那么光电耦合器的工作原理是什么呢?要了解光电耦合器的原理，首先就要了解它的组成部分。光电耦合器主要是由两部分组成，分别是发光源和受光器，这两部分的元件都同时处于一个密闭的空间中，而且彼此之间都是用绝缘的透明壳体隔离。电流工作的方式是以发光源的接线口为输入端，电流从这里进入。以受光器的接线口为输出端，电流从这里输出。当电流进入到发光源中，发光的元件受到电流作用发光，而且光的亮度会因为输入电流的大小而改变。当光照到受光器上，受光器发生反应，电流从这里输出就会成为光电流。 那么什么是光电流呢?它是同时具有光电特性的信号，当这种信号传播到受光器上，受光器就会根据光电流的光照强度输出对应大小的电流，这些电流再回到电路中，就会形成一
1、传导耦合 导线经过有干扰的环境，即拾取干扰信号并经导线传导到电路而造成对电路的干扰，称为传导耦合，或者叫直接耦合。 在音频和低频的时候由于电源线、接地导体、电缆的屏蔽层呈现低阻抗，故电流注入这些导体时容易传播，当噪声传导到其他敏感电路的时候，就能产生干扰作用。 在高频的时候：导体的电感和电容将不容忽视，感抗随着频率的增加而增加，容抗随着频率的增加而减小。jwL,1/jwC 解决方法:防止导线的感应噪声，即采用适当的屏蔽和将导线分离，或者在骚扰进入明暗电路之前，用滤波的方法将其从导线中除去； 2、共阻抗耦合 当两个电路的电流经过一个公共阻抗时，一个电路的电流在该公共阻抗上形成的电压就会影响到另一个电路。 3、感应耦合 a）电感应容性耦合 干扰电路的端口电压会导致干扰回路中的电荷分布，这些电荷产生电场的一部分会被敏感电路拾取，当电场随时间变化，敏感回路中的时变感应电荷就会在回路中形成感应电流，这种叫做电感应容性耦合。 解决方法：减小敏感电路的电阻值，改变导线本身的方向性屏蔽或者分隔来实现。 b）磁感应耦合 干扰回路中的电流产生的磁通密度的一部分会被其他回路拾取，当磁通密度随时间变化时就会在敏感回路中出现感应电压，这种回路之间的耦合叫做磁感应耦合。 主要形式：线圈和变压器耦合、平行双线间的耦合等。铁心损耗常常使得变压器的作用类似于抑制高频干扰的低通滤波器。平行线间的耦合是磁感应耦合的主要形式 要想减少干扰，必须尽量减少两导线之间的互感。 4、辐射耦合 辐射源向自由空间传播电磁波，感应电路的两根导线就像天线一样，接受电磁波，形成干扰耦合。干扰源距离敏感电路比较近的时候，如果辐射源有低电压大电流，则磁场起主要作用；如果干扰源有高电压小电流，则电场起主要作用。 对于辐射形成的干扰，主要采用屏蔽技术来抑制干扰。
star法则成就故事例文 【--党风廉政建设】 在求职的时候我们会遇到各种各样的面试官，如何在面对不同面试官时都能从容的应对是很多人思考的问题，除了做好充分的准备之外，还需要了解star法则，因为它同基本企业管理中的十大定律一样是面试官常用的，而今天我们就来介绍几个star法则成就故事例文。本站为大家整理的相关的star法则成就故事例文，供大家参考选择。 star法则成就故事例文 什么叫star法则 首先我们需要先了解star法则的意思。所谓star法则是指情境、任务、行动、结果四个词的缩写，其中情境是指事情是在什么情况下发生的;任务是指你是如何明确任务的;行动是指针对这样的情况分析后采取了什么样的行动方式;结果是指最后取得什么样的结果并且学习到了什么。 如果将四项连接起来，star法则可以理解为：案例在什么情况下发生发生之后当事人如何明确案例中给到自己的任务对任务进行分析然后采取对应的行动最后取得什么样的结果并且从中学习到什么，简单的来说它就是一种让面试者讲述自己故事的方式，可以看出面试者阐述问题时的条理性和逻辑性等等。 star法则成就故事例文 用STAR法来撰写成就故事 请写下生活中令你有成就感的具体事件然后对其进行分析，看看你在其中使用了那些技能(尤其是可迁移技能)。 这些成就故事不一定是在工作或学习上的，也可以是课外活动或家庭生活中发生的，比如同学聚会，一次美好而难忘的旅游等等，他们不必是惊天动地的大事，只要符合两条标准就可以被视为成就 (1)你喜欢做这件事时体验到的感受 (2)你为完成他所带来的结果感到自豪。 如果你同时还获得了他人的认可和表扬那就更好了，不过这并不重要。 在撰写成就故事时，每一个故事都应当包含一下要素： 当时的情况(Situation)
STAR法则详解 一.什么是STAR法则? The STAR (Situation, Task, Action, Result) format is a job interview technique used by interviewers to gather all the relevant information about a specific capability that the job requires. This interview format is said to have a higher degree of predictability of future on-the-job performance than the traditional interview. STAR法则是情境(situation)、任务(task)、行动(action)、结果(result)四项的缩写。STAR法则是一种常常被官使用的工具，用来收集面试者与工作相关的具体信息和能力。STAR法则比起传统的面试手法来说，可以更精确地预测面试者未来的工作表现。
Situation: The interviewer wants you to present a recent challenge and situation in which you found yourself. 情境：面试官希望你能描述一个最近遇到的挑战或情况。 T ask: What did you have to achieve? The interviewer will be looking to see what you were trying to achieve from the situation. 任务：你必须要完成什么任务?面试者想要知道的是你在上述情境下如何去明确自己的任务。 Action: What did you do? The interviewer will be looking for information on what you did, why you did it and what were the alternatives.
指导 预习课本第三章，根据课本P61页的小练习为例， 用STARL法来编写三个成就故事： 1）S：Situation(情境，背景）“在什么情景下发生的？” 2）T：Task(任务）“当时你的任务和目标是什么？” 3）A：Action(行动）“你采取了哪些行动？” 4）R：Result(结果）“最后结果怎么样？” 5）L：Learning(学习）：“我从中学到了…” 内容包括：专业技能；可迁移技能；自我管理技能三种。 （请直接打字或粘贴，不要用附件形式) 成就故事一： 这个是我第一次从商的故事，发生在我上高一时的寒假。当时马上就要过新年了，也正是那时苹果最好卖，每年都是那时家里的苹果拉到省城批发，可是那一年父亲在忙着准备过年的物资，没法出去卖苹果。于是，我爸就叫我去，当时我是不愿意去的，心里也害怕，但是我爸说他像我这个年纪的时候就快成家了，把我训了一顿。因此，有了我第一次外出卖苹果的经历。由于我是第一次出去，就只拉了2000斤苹果，让我自己看着卖，就这样自己跟随货车到了省城。在水果批发市场我第一次感受到了挣钱不容易，好多商贩看我年纪小过来坑我，好在我出来时，对价格有了大概的了解，没被唬住。在闲时，我就向别人请教，问问他们怎么卖的怎
么对付商贩的胡搅蛮缠。渐渐地，我也有了自己的方法，那就是说话要硬气，有底气，去唬他们，让商贩跟着自己的节奏走。在那呆了三天，我就把家里的苹果批发完了，当时心里可激动了。在以后，放假回家，就由我代替父亲去省城卖水果。当时我就体会到了父亲的用意，男孩子就需要磨练，只有迈出第一步，才会有第二步......自己才有勇气独立面对以后的生活。 我认识到，在生活中，要大胆尝试，自己不去做，永远不知道自己有多优秀。从这，我就开始慢慢脱离学生时代的幼稚天真，慢慢接触社会。从我开口与商贩周旋的时候我就体会到做人要有自信，有底气，只有这样，别人才不会小瞧你，有时，会有不错的效果，当你的自信占了上风，你离成功就不远了。 成就故事二： 我的第二个成就故事是大一暑假自己出去打工。当时，学校放假早，我不打算早早回家，于是瞒着父母自己找工作，开始的时候打算跟着同学一起去山东青岛，后来人家招满了人，就没去成。我在学校留了两天，听说富士康招人就打算去看看，在体检的时候我改变了主意，决定离开。我经过多方打听知道，那年电子市场不景气厂里没有多少活做，老工人都没多少活做，更何况我们这些学生工。因此我再次回到
液力偶合器的作用和工作原理 1)作用和意义 在转炉生产过程中，吹炼时间和非吹炼时间约各占一半，在非吹炼时期，没有炉气产生，因此转炉除尘系统的风机是长期处在一种间歇操作的负荷下工作，为了适应转炉的生产情况，在除尘风机与电机之间设置液力偶合器，控制风机在非吹炼时间内处于低转速运转，风机的轴功率可降低到25％左右，大大的节约了非吹炼时间的电力消耗。 液力偶合器工作平稳，它可以消除来自风机或电机的冲击和震动。当风机起动时，将风机调到低转速的位置，这样可以减小其起动力矩和起动过载电流。为了减少风机叶轮的积灰与震动，可在低转速下进行叶轮的水冲洗，从而改善风机与电机的工作条件提高其使用寿命。 在非吹炼时间，风机处于低转速运转，冷空气的吸入量就大大减少，使冷空气带走汽化冷却器的热损失也相应减少，同时也减轻了汽化冷却器的水管外壁骤冷骤热的程度，从而改善了汽化冷却器的运行条件，其使用寿命也可相应提高。 2)工作原理 液力偶合器又名动液偶合器、透平离合器或液压联动联轴节。它是利用液体用为工作介质来传递功率的，它的构造是由带有径向叶片的泵轮和涡轮两个部分组成。如图5－29所示，当电动机带动其泵轮转动后，泵轮便带着腔体内的工作液体同时旋转。旋转的液体便随即带动其涡轮也转动起来，如果涡轮的出轴与风机连接，则风机也跟着转动。假若此时将腔体内的工作液体全部排除，涡轮的转动也就随即停止，风机便停止运转，同时也可采用各种调速的方法使涡轮在最低稳定转速到最大转速范围内以任意转速旋转。 液力偶合器的腔型，可分为单腔和双腔两种。 ①单腔：结构简单，外形较小，但轴向推力大。 ②双腔：如图5—29所示；轴向推力小，但结构比较复杂。外形较大。 图5－29 双腔液力偶合器节流阀调节系统 液力偶合器的调速方式，主要可分下列四种： ①利用外部供油管道上的节流阀来调节油腔的油量。如图5－29所示； ②利用伸入油腔内的勺管来调节油腔的出油量。 ③用改变环流通道的几何形状的方法来调节其涡轮的转速。 ④利用转动叶片的方法，来调节涡轮的转速。 上述四种调速方式中的第1、2两种使用比较普遍，都是利用改变油腔内油的充满率来实现的，可以近似地认为偶合器的特性曲线，是随着油的充满率的变化而有规律地改变，当充满率减小时，液力偶合器的转速也随之减少。中国冶金行业网
STAR法则,500强面试题回答时的技巧法则,备受面试者成功者和500强HR的推崇（宝洁HR培训资料有专门的讲座讨论如何用此法则检验面试者过往事迹从而判断其能力）。 如果对面试技巧和人力资源招聘理论有所了解的同学应该听说过,没听说也无所谓,现在知道也不迟。由于这个法则被广泛应用于面试问题的回答，尽管我们还在写简历阶段，但是，写简历时能把面试的问题就想好，会使自己更加主动和自信，做到简历，面试关联性，逻辑性强，不至于在一个月后去面试，却把简历里的东西都忘掉了（更何况有些朋友会稍微夸大简历内容） 废话少说，开讲。 在我们写简历时，每个人都要写上自己的工作经历，活动经历，想必每一个同学，都会起码花上半天甚至更长的时间去搜寻脑海里所有有关的经历，争取找出最好的东西写在简历上。 但是此时，我们要注意了，简历上的任何一个信息点都有可能成为日后面试时的重点提问对象，所以说，不能只管写上让自己感觉最牛的经历就完事了，要想到今后，在面试中，你所写的经历万一被面试官问到，你真的能回答得流利，顺畅，且能通过这段经历，证明自己正是适合这个职位的人吗？ 所以，写简历时就要准备好面试时的个人故事，以便应付各种千奇百怪的开放性问题。 为了使大家轻松应对这一切，我向大家推荐“个人事件模块”的方法，以使自己迅速完成这看似庞大的工程。 一，头脑风暴＋STAR法则——〉个人事件模块 1．1，头脑风暴。 在脑海里仔细想出从大一到大四自己参与过所有活动（尤其是能突出你某些能力的活动），包括： 社团活动职务时间所做事情 在公司实习的经历职务时间所做过的事情 与他人一起合作的经历（课题调研，帮助朋友办事） （回忆要尽量的详细，按时间倒序写在纸上，如大一上学期发生。。。。。。大一下学期发生。。。。。。。如此类推） 我相信这一步，很多朋友都已经做了，但是仅仅这样就满足了，就直接写在简历上当完事了，那是不行的，想提高竞争力，还得继续。。 1．2，STAR法则应用