An analysis of V photometric light curves of the eclipsing cataclysmic variable SDSS J150240.98+333423.9/NZ Boo obtained in April-June, 2012 with a CCD photometer using the 60-cm telescope of the Sternberg Astronomical Institute's Crimean station is presented (based on more than 750 images). The first observation was made ~350-370 orbital cycles after the beginning of the outburst of April 2012; all the observations correspond to quiescence of the system. The orbital period, P = 0.0589106(4)d, changed by no more than {Delta}Porb/Porb~2x10^-5^ during the more than 37200 orbital cycles since the previous observations of the system.
We present the first results from our survey of the star-forming complex W3, combining VRI photometry with multiobject spectroscopy to identify and characterize the high-mass stellar population across the region. With 79 new spectral classifications, we bring the total number of spectroscopically confirmed O- and B-type stars in W3 to 105. We find that the high-mass slope of the mass function in W3 is consistent with a Salpeter IMF, and that the extinction toward the region is best characterized by an R_V_ of approximately 3.6. B-type stars are found to be more widely dispersed across the W3 giant molecular cloud (GMC) than previously realized: they are not confined to the high-density layer (HDL) created by the expansion of the neighboring W4 H ii region into the GMC. This broader B-type population suggests that star formation in W3 began spontaneously up to 8-10 Myr ago, although at a lower level than the more recent star formation episodes in the HDL. In addition, we describe a method of optimizing sky subtraction for fiber spectra in regions of strong and spatially variable nebular emission.
The catalog contains the ultraviolet photometry of 531 stars observed with the Wisconsin Experiment Package aboard the Orbiting Astronomical Observatory (OAO-2). The data were obtained with medium-band interference filters and have been reduced to a uniform magnitude system. The ultraviolet magnitudes contained in the catalog have been published by Code et al. (1980). While the published tables contain 11 tabulated magnitudes, the machine version includes a twelfth filter (S2F2 at 2945 A). The catalog includes cross identifications to the numbering systems of the Bright Star Catalogue, The Henry Draper Catalogue, and the GC, star name, spectral type, V magnitude, B-V, U-B, references, remarks, and 12 ultraviolet magnitudes. The effective wavelengths (for a flat spectrum source) are 4250A, 3320A, 2980A, 2965A, 2460A, 2380A, 2035A, 1910A, 1680A, 1550A, 1430A, and 1330A. For most filters, the full width, half maximum is about 30% of the central wavelength.
The Multicolor Simultaneous Camera for studying Atmospheres of Transiting exoplanets (MuSCAT) is an optical three-band (g'_2_-, r'_2_- and z_s,2_-band) imager that was recently developed for the 188cm telescope at Okayama Astrophysical Observatory with the aim of validating and characterizing transiting planets. In a pilot observation with MuSCAT we observed a primary transit of HAT-P-14b, a high-surface gravity (g_p_=38ms^-2^) hot Jupiter around a bright (V=10) F-type star. From a 2.9hr observation we achieved the five-minute binned photometric precisions of 0.028%, 0.022%, and 0.024% in the g'_2_, r'_2_, and z_s,2_ bands, respectively, which provided the highest-quality photometric data for this planet. Combining these results with those of previous observations, we search for variations of transit timing and duration over five years as well as variations of planet-star radius ratio (Rp/Rs) with wavelengths, but can find no considerable variation in any parameters. On the other hand, using the transit-subtracted light curves we simulate the achievable measurement error of Rp/Rs with MuSCAT for various planetary sizes, assuming three types of host stars: HAT-P-14, the nearby K-dwarf HAT-P-11, and the nearby M-dwarf GJ1214. Comparing our results with the expected atmospheric scale heights, we find that MuSCAT is capable of probing the atmospheres of planets as small as a sub-Jupiter (Rp~6R_{earth}_) around HAT-P-14 in all bands, a Neptune (~4R_{earth}_) around HAT-P-11 in all bands, and a super-Earth (~2.5R_{earth}_) around GJ1214 in r'_2_ and z_s,2_ bands. These results promise that MuSCAT will produce fruitful scientific outcomes in the K2 and TESS era.
This file contains UBV photometry for the brightest stars in the southern spiral arm of M33. All stars brighter than V=21 are included in this file. For details on the observations and data reduction see reference. All the data is in ASCII format of the file. The observations where carried out on the Palomar 60in. telescope.
Images of the central and southern parts of the local group Sb spiral galaxy M31 were obtained by the Ultraviolet Imaging Telescope during the Astro-1 Spacelab mission. Stellar photometry is obtained for 611 stars in 59 van den Bergh associations in the near-UV A1 band (central wavelength 2490A), and for 130 of these stars in the far-UV B1 band (central wavelength 1520A). In addition, B-band magnitudes for 456 of the stars in ~30 associations, together with U- and R-band photometry for ~290 stars in ~15 associations are determined from CCD images. B-magnitudes from the catalog of Magnier et al. (1992A&AS...96..379M) are given for 137 stars and R-magnitudes for 233 stars. Stellar positions are obtained from the ground-based CCD images and from UIT images. Total fluxes in the UV bands are measured for 63 associations. Finding charts are presented in the NUV and FUV bands, as well as one optical band. Tables give the images utilized in this investigation, the associations observed, with positions, total UV fluxes, extinctions estimated from color-magnitude diagrams, and stellar positions with photometry in up to five bands. UV color magnitude diagrams are presented with extinctions estimated by comparing the observed association color magnitude diagrams with colors and magnitudes of early-type stars computed from the IUE spectral atlas of Fanelli et al. (1992ApJS...82..197F). Comparison with evolutionary models suggests a maximum initial mass ~85M_{sun}_. Ultraviolet extinction within most M31 OB associations is found to follow an extinction curve similar to that of Hutchings et al. (1992ApJ...400L..35H). The variation in the fraction of near-UV stars also measured in the far-UV among the associations is probably caused by variations in age, extinction, and the degree of foreground contamination.
We report on the results from application of an objective algorithm (PLC) to find OB associations, to B and V images of the Sculptor spiral galaxy NGC 7793, which were obtained with the ESO VLT and FORS instrument and basically cover the entire spatial extent of the galaxy. We detected 148 associations. Statistical tests show that less than 6 of these detections are caused by randomly concentrated blue stars. In the size distribution, a sharp peak is observed at a value of about 35 microradians, which corresponds to a linear diameter of 135pc, assuming a distance of 3.91Mpc to the galaxy. We also find 25 much larger objects. A second application of the PLC technique shows that 20 of them are stellar complexes consisting of multiple sub-associations with typical sizes on the order of 130pc. A comparison of the size distribution of the detected OB associations in NGC 7793 with observed distributions in other galaxies suggests that the conditions in two Sculptor Group galaxies (NGC 300 and NGC 7793) favour the formation of large associations. We provide a catalog giving coordinates and physical parameters for all the associations and stellar complexes we have found in our survey.
We investigate the massive star content of Milky Way clusters and OB associations in order to answer three questions: (1) How coeval is star formation? (2) How constant is the initial mass function (IMF)? (3) What is the progenitor mass of Wolf-Rayet stars? Our sample includes NGC 6823/Vul OB1, NGC 6871/Cyg OB3, Berkeley 86/Cyg OB1, NGC 6913/Cyg OB1, NGC 7235, NGC 7380/Cep OB1, Cep OB5, IC 1805/Cas OB6, NGC 1893/Aur OB2, and NGC 2244/Mon OB2. Large-field CCD imaging and multiobject, fiber spectroscopy has resulted in UBV photometry for >10,000 stars and new spectral types for ~200 stars. These data are used to redetermine distances and reddenings for these regions and to help exclude probable nonmembers in constructing the H-R diagrams. We reanalyze comparable data previously published on Cyg OB2, Tr 14/16, and NGC 6611 and use all of these to paint a picture of star formation and to measure the IMFs. We find the following: (1) Most of the massive stars are born during a period Delta(Tau) < 3 Myr in each association. Some star formation has clearly preceded this event, as evidenced by the occasional presence of evolved (Tau ~ 10 Myr) 15 Msun stars despite a typical age Tau ~ 2 Myr for the more massive population. However, all these regions also show evidence of 5-10 Msun pre-main-sequence stars (Tau < 1 Myr), demonstrating that some star formation at lower masses does continue for at least 1 Myr after the formation of high-mass stars. (2) There is no statistically significant difference in IMF slopes among these clusters, and the average value is found to be Gamma = -1.1 +/- 0.1 for stars with masses > 7 Msun. A comparison with similarly studied OB associations in the Magellanic Clouds reveals no difference in IMF slope, and hence we conclude that star formation of massive stars in clusters proceeds independently of metallicity, at least between z = 0.02 and z = 0.002. The masses of the highest mass stars are approximately equal in the Milky Way, LMC, and SMC associations, contrary to the expectation that this value should vary by a factor of 3 over this metallicity range. We conclude that radiation pressure on grains must not limit the mass of the highest mass star that can form, in accord with the suggestion of Wolfire & Cassinelli that the mere existence of massive stars suggests that shocks or other mechanisms have disrupted grains in star-forming events. (3) The four Wolf-Rayet stars in our sample have come from stars more massive than 40 Msun; one WC star and one late-type WN star each appear to have come from very massive (~100 Msun) progenitors.
Since the release of the Hipparcos catalogue in 1997, the distance to the Pleiades open cluster has been heavily debated. The distance obtained from Hipparcos and those by alternative methods differ by 10 to 15%. As accurate stellar distances are key to understanding stellar structure and evolution, this dilemma puts the validity of some stellar evolution models into question. Using our model-independent method to determine parallaxes based on twin stars, we report individual parallaxes of 15 FGK type stars in the Pleiades in anticipation of the astrometric mission Gaia. These parallaxes give a mean cluster parallax of 7.42+/-0.09mas,which corresponds to a mean cluster distance of 134.8+/-1.7pc. This value agrees with the current results obtained from stellar evolution models.
We carried out photometric and low-resolution spectral observations of six eclipsing ultrashort-period binaries with main-sequence (MS)components. The light-curve solutions of the Rozhen observations show that all targets are overcontact systems. We found a well-defined empirical relation between period and semi-major axis for the short-period binaries and used it for estimation of the global parameters of the targets. Our results revealed that NSVS 925605 is quite an interesting target: (i) it is one of a few contact binaries with M components; (ii) it exhibits high activity (emission in the H{alpha} line, X-ray emission, large cool spots, non-Planck energy distribution); (iii) its components differ in temperature by 700 K. All the appearances of high magnetic activity and the huge fill-out factor (0.7) of NSVS 925605 may be a precursor of the predicted merging of close magnetic binaries. Another unusual binary is NSVS 2700153, which reveals considerable long-term variability.
