UBV photometry and moderate resolution H{alpha} spectrophotometry of the evolved binary system HD 185510 (sdB + K0 III), performed at Catania Astrophysical Observatory, is presented and discussed. The spectrophotometric data were collected in 1991, 1993, and 1994, while the photometric light curves were obtained in 1993, 1994 and 1995. From the B and V photometry we determine a new photometric rotational period of 26.23d, confirming the asynchronous rotation of the cool giant component. The spectroscopic data confirm the vsin i value of 15km/s measured by Fekel et al. (1993AJ....106.2370F) and clearly reveal a filled-in H{alpha} line with appreciable variations. The excess emission of the line, observed at any orbital phase, is found to be anticorrelated with the V light curve and is primarily ascribed to the chromospheric activity on the cool star. The primary total eclipse is clearly visible in the U band, but undetectable in the V band. From the U observations we determined a total duration of the primary eclipse (from 1^st^ to 4^rd^ contact) of 1.3883d, with the ingress lasting only 27 minutes. This new accurate monitoring and timing of the eclipse allowed us to improve the system solution which leads to R_C_=8.8R_{sun}_, T_C_=4800K, R_H_=0.11R_{sun}_, T_H_=30000K for the cool and hot star respectively. The evolution of HD 185510B is discussed also in relation to the evolutionary status of HD 185510A and the synchronization time scale. HD 185510B is probably a sdB near the zero age extended horizontal branch, resulting from an enhanced mass loss in late case B or case A mass exchange with a possible common envelope phase. A small amount (15-20%) of mass loss from the system which can account for the strong IR excess is suggested.
We present spectroscopic and photometric observations of the star HD 173977. It appears that the star is part of a double line binary system, with a period of 1.801d, corresponding to twice the period of the photometric variations. Hence the star is an ellipsoidal variable. The system is probably synchronized. The physical parameters of both components were derived through two independent methods, one based on evolutionary tracks, the other being the result of the behaviour of light curves in a close binary system. After removing the ellipsoidal variations, 3 frequencies are detected in the photometric data: 8.56, 14.51 and 16.42d^-1^, while 2 additional frequencies are also possible: 10.96 and 12.11d^-1^. In accordance with its position in the HR diagram, the primary component of HD 173977 should be considered as a delta Scuti star and no longer as a gamma Doradus star. In addition, HD 173844, used as a check star, is discovered variable with a 15.79d^-1^ frequency and is classified as a delta Scuti star.
The existence of a significant population of Ap stars with very long rotation periods (up to several hundred years) has progressively emerged over the past two decades. However, only lower limits of the periods are known for most of them because their variations have not yet been observed over a sufficient timebase. We determine the rotation period of the slowly rotating Ap star HD 18078 and we derive constraints on the geometrical structure of its magnetic field. We combine measurements of the mean magnetic field modulus obtained from 1990 to 1997 with determinations of the mean longitudinal magnetic field spanning the 1999-2007 time interval to derive an unambiguous value of the rotation period. We show that this value is consistent with photometric variations recorded in the Stromgren uvby photometric system between 1995 and 2004. We fit the variations of the two above-mentioned field moments with a simple model to constrain the magnetic structure.
The gravitationally lensed quasar HE 1104-1805 has been observed at a variety of wavelengths ranging from the mid-infrared to X-ray for nearly 20yr. We combine flux ratios from the literature, including recent Chandra data, with new observations from the SMARTS telescope and Hubble Space Telescope, and use them to investigate the spatial structure of the central regions using a Bayesian Monte Carlo analysis of the microlensing variability. The wide wavelength coverage allows us to constrain not only the accretion disk half-light radius r_1/2_, but the power-law slope {xi} of the size-wavelength relation r_1/2_{prop.to}{lambda}^{xi}^. With a logarithmic prior on the source size, the (observed-frame) R-band half-light radius log (r_1/2_/cm) is 16.0_-0.4_^+0.3^, and the slope {xi} is 1.0_-0.56_^+0.30^. We put upper limits on the source size in soft (0.4-1.2 keV) and hard (1.2-8keV) X-ray bands, finding 95% upper limits on log (r_1/2_/cm) of 15.33 in both bands. A linear prior yields somewhat larger sizes, particularly in the X-ray bands. For comparison, the gravitational radius, using a black hole mass estimated using the H{beta} line, is log(r_g_/cm)=13.94. We find that the accretion disk is probably close to face-on, with cos(i)=1.0 being four times more likely than cos(i)=0.5. We also find probability distributions for the mean mass of the stars in the foreground lensing galaxy, the direction of the transverse peculiar velocity of the lens, and the position angle of the projected accretion disk's major axis (if not face-on).
We use dense redshift surveys to explore the properties of galaxy clusters selected from the redMaPPer catalog. Our new survey, Hectospec Cluster Survey of red-sequence-selected clusters (HeCS-red), includes 10589 new or remeasured redshifts from MMT/Hectospec observations of 27 redMaPPer clusters at redshifts z=0.08-0.25 with large estimated richnesses (richness estimate {lambda}>64). Our spectra confirm that each candidate cluster corresponds to a large overdensity in redshift space. The redMaPPer photometric redshifts have a slight bias toward higher redshifts. We measure the relation between velocity dispersion {sigma}p and {lambda}. The relation shows intrinsic scatter of 24% (and a range of 2x) in velocity dispersion at fixed richness. We extend our analysis to HeCS-red-ext, a sample that includes several clusters selected by X-ray flux or Sunyaev-Zeldovich signal. The heterogeneous sample of 121 clusters in HeCS-red-ext shows similar intrinsic scatter in the {sigma}p-{lambda} relation as the HeCS-red sample, but the range of {sigma}p at fixed richness increases to 3x. We evaluate the membership probability estimates Pmem for individual galaxies provided by redMaPPer. The spectroscopic membership fraction is larger than Pmem for 0.05<=P_mem_<=0.7; conversely, the spectroscopic membership fraction is smaller than P_mem_ at P_mem_>=0.8. We compare spectroscopic richness estimates with redMaPPer richness estimates and find good agreement on average, but a range of a factor of two in spectroscopic richness at fixed redMaPPer richness. Overall, within the high-richness and low-redshift cut of our sample, spectroscopically estimated parameters such as velocity dispersion correlate well with photometric richness estimates, although the relations contain substantial scatter.
We calibrated a technique to measure dust attenuation in star-forming galaxies. The technique utilizes the stellar-wind lines in Wolf-Rayet stars, which are widely observed in galaxy spectra. The He II 1640 and 4686 features are recombination lines whose ratio is largely determined by atomic physics. Therefore they can serve as a stellar dust probe in the same way as the Balmer lines are used as a nebular probe. We measured the strength of the He II 1640 line in 97 Wolf-Rayet stars in the Galaxy and the Large Magellanic Cloud. The reddening corrected fluxes follow a tight correlation with a fixed ratio of 7.76 for the He II 1640 to 4686 line ratio. Dust attenuation decreases this ratio. We provide a relation between the stellar E(B-V) and the observed line ratio for several attenuation laws. Combining this technique with the use of the nebular Balmer decrement allows the determination of the stellar and nebular dust attenuation in galaxies and can probe its effects at different stellar age and mass regimes, independently of the initial mass function and the star formation history. We derived the dust reddening from the He II line fluxes and compared it to the reddening from the Balmer decrement and from the slope of the ultraviolet continuum in two star-forming galaxies. The three methods result in dust attenuations which agree to within the errors. Future application of this technique permits studies of the stellar dust attenuation compared to the nebular attenuation in a representative galaxy sample.
The HeII transverse proximity effect-enhanced HeII Ly{alpha} transmission in a background sightline caused by the ionizing radiation of a foreground quasar-offers a unique opportunity to probe the morphology of quasar-driven HeII reionization. We conduct a comprehensive spectroscopic survey to find z~3 quasars in the foreground of 22 background quasar sightlines with Hubble Space Telescope/COS HeII Ly{alpha} transmission spectra. With our two-tiered survey strategy, consisting of a deep pencil-beam survey and a shallow wide-field survey, we discover 131 new quasars, which we complement with known SDSS/BOSS quasars in our fields. Using a restricted sample of 66 foreground quasars with inferred HeII photoionization rates greater than the expected UV background at these redshifts ({Gamma}_QSO_^HeII^>5x10^-16^s^-1^) we perform the first statistical analysis of the HeII transverse proximity effect. Our results show qualitative evidence for a large object-to-object variance: among the four foreground quasars with the highest {Gamma}_QSO_^HeII^ only one (previously known) quasar is associated with a significant HeII transmission spike. We perform a stacking analysis to average down these fluctuations, and detect an excess in the average HeII transmission near the foreground quasars at 3{sigma} significance. This statistical evidence for the transverse proximity effect is corroborated by a clear dependence of the signal strength on {Gamma}_QSO_^HeII^. Our detection places a purely geometrical lower limit on the quasar lifetime of t_Q_>25Myr. Improved modeling would additionally constrain quasar obscuration and the mean free path of HeII-ionizing photons.
We present an analysis of 1023 DBZ/DZ(A) and 319 DQ white dwarf stars taken from the Montreal White Dwarf Database. This represents a significant increase over the previous comprehensive studies on these types of objects. We use new trigonometric parallax measurements from the Gaia second data release, together with photometry from the Sloan Digital Sky Survey, Pan-STARRS, Gaia, or BVRI from the literature, which allow the determination of the mass for the majority of the objects in our sample. We use the photometric and spectroscopic techniques with our recently improved model atmospheres code, which include high-density effects, to accurately determine the effective temperature, surface gravity, and heavy-element abundances for each object. We study the abundance of hydrogen in DBZ/DZ white dwarfs and the properties of the accreted planetesimals. We explore the nature of the second sequence of DQ stars using proper motions from Gaia and highlight evidence of crystallization in massive DQ stars. We also present mass distributions for both spectral types. Finally, we discuss the implications of our findings in the context of the spectral evolution of white dwarfs and provide the atmospheric parameters for each star.
UBVR photometric monitoring of Herbig Ae/Be stars and some related objects has been carried out at Maidanak Observatory in Uzbekistan since 1983. More than 71,000 observations of about 230 stars have been obtained and are made available for anonymous ftp. Virtually all Herbig Ae/Be stars observed are irregular variables (called "UXors" after UX Ori), but there is a wide range of amplitudes from barely detectable to more than 4mag in V. Our data confirm the results of previous studies, which indicate that large-amplitude variability is confined to stars with spectral types later than B8. The distribution of variability ranges is quite similar to what is seen in classical T Tauri stars.
The intriguing binary LS V +22 25 (LB-1) has drawn much attention following claims of it being a single-lined spectroscopic binary with a 79-day orbit comprising a B-type star and a ~70M_{sun}_ black hole - the most massive stellar black hole reported to date. Subsequent studies demonstrated a lack of evidence for a companion of such great mass. Recent analyses have implied that the primary star is a stripped He-rich star with peculiar sub-solar abundances of heavy elements, such as Mg and Fe. However, the nature of the secondary, which was proposed to be a black hole, a neutron star, or a main sequence star, remains unknown. Based on 26 newly acquired spectroscopic observations secured with the HERMES and FEROS spectrographs covering the orbit of the system, we perform an orbital analysis and spectral disentangling of LB-1 to elucidate the nature of the system. To derive the radial velocity semi-amplitude K2 of the secondary and extract the spectra of the two components, we used two independent disentangling methods: the shift-and-add technique and Fourier disentangling with FDBinary. We used atmosphere models to constrain the surface properties and abundances. Our disentangling and spectral analysis shows that LB-1 contains two components of comparable brightness in the optical. The narrow-lined primary, which we estimate to contribute 55% in the optical, has spectral properties that suggest that it is a stripped star: it has a small spectroscopic mass (~1M_{sun}_) for a B-type star and it is He- and N-rich. Unlike previous reports, the abundances of heavy elements are found to be solar. The 'hidden' secondary, which contributes about 45% of the optical flux, is a rapidly rotating (vsini~300km/s) B3 V star with a decretion disk - a Be star. As a result of its rapid rotation and dilution, the photospheric absorption lines of the secondary are not readily apparent in the individual observations.We measure a semi-amplitude for this star of K2=11.2+/-1.0km/s and adopting a mass of M2=72M_{sun}_ typical for B3 V stars, we derive an orbital mass for the stripped primary of M1=1.5+/-0.4 M_{sun}_. The orbital inclination of 394 implies a near-critical rotation for the Be secondary (v_eq_~470km/s). LB-1 does not contain a compact object. Instead, it is a rare Be binary system consisting of a stripped star (the former mass donor) and a Be star rotating at near its critical velocity (the former mass accretor). This system is a clear example that binary interactions play a decisive role in the production of rapid stellar rotators and Be stars.
