RAT0455+1305: another pulsating hybrid sdB star

RAT0455+1305 was discovered during the Rapid Temporal Survey which aims in finding any variability on timescales of a few minutes to several hours. The star was found to be another sdBV star with one high amplitude mode and relatively long period. These features along with estimation of T_eff and log g makes this star very similar to Balloon 090100001. Encouraged by prominent results obtained for the latter star we have decided to perform white light photometry on RAT0455+1305. In 2009 we used the 1.5m telescope located in San Pedro Martir Observatory in Mexico. Fourier analysis confirmed the dominant mode found in the discovery data, uncovered another peak close to the dominant one, and three peaks in the low frequency region. This shows that RAT0455+1305 is another hybrid sdBV star pulsating in both p- and g-modes.Comment: Proceedings of The Fourth Meeting on Hot Subdwarf Stars and Related Objects held in China, 20-24 July 2009. Accepted for publication in Astrophysics & Space Scienc

A Dusty Disk Around WD1150-153: Explaining the Metals in White Dwarfs by Accretion from the Interstellar Medium versus Debris Disks

We report the discovery of excess K-band radiation from a metal-rich DAV white dwarf star, WD1150-153. Our near infrared spectroscopic observations show that the excess radiation cannot be explained by a (sub)stellar companion, and is likely to be caused by a debris disk similar to the other DAZ white dwarfs with circumstellar debris disks. We find that the fraction of DAZ white dwarfs with detectable debris disks is at least 14%. We also revisit the problem of explaining the metals in white dwarf photospheres by accretion from the interstellar medium (ISM). We use the observed interstellar column densities toward stars in close angular proximity and similar distance as DAZ white dwarfs to constrain the contribution of accretion from the ISM. We find no correlation between the accretion density required to supply metals observed in DAZs with the densities observed in their interstellar environment, indicating that ISM accretion alone cannot explain the presence of metals in nearby DAZ white dwarfs. Although ISM accretion will certainly contribute, our analysis indicates that it is not the dominant source of metals for most DAZ white dwarfs. Instead, the growing number of circumstellar debris disks around DAZs suggests that circumstellar material may play a more dominant role in polluting the white dwarf atmospheres.Comment: ApJ, in pres

Evaluation of Weight Change During Carboplatin Therapy in Dogs With Appendicular Osteosarcoma.

BackgroundThe prevalence of cancer cachexia in veterinary medicine has not been studied widely, and as of yet, no definitive diagnostic criteria effectively assess this syndrome in veterinary patients.Objectives(1) To determine the patterns of weight change in dogs with appendicular osteosarcoma treated with amputation and single-agent carboplatin during the course of adjuvant chemotherapy; and (2) to determine whether postoperative weight change is a negative prognostic indicator for survival time in dogs with osteosarcoma.AnimalsEighty-eight dogs diagnosed with appendicular osteosarcoma. Animals were accrued from 3 veterinary teaching hospitals.MethodsRetrospective, multi-institutional study. Dogs diagnosed with appendicular osteosarcoma and treated with limb amputation followed by a minimum of 4 doses of single-agent carboplatin were included. Data analyzed in each patient included signalment, tumor site, preoperative serum alkaline phosphatase activity (ALP), and body weight (kg) at each carboplatin treatment.ResultsA slight increase in weight occurred over the course of chemotherapy, but this change was not statistically significant. Weight change did not have a significant effect on survival. Institution, patient sex, and serum ALP activity did not have a significant effect on survival.Conclusions and clinical importanceWeight change was not a prognostic factor in these dogs, and weight loss alone may not be a suitable method of determining cancer cachexia in dogs with appendicular osteosarcoma

Orbital Characteristics of the Subdwarf-B and F V Star Binary EC~20117-4014(=V4640 Sgr)

Among the competing evolution theories for subdwarf-B (sdB) stars is the binary evolution scenario. EC~20117-4014 (=V4640~Sgr) is a spectroscopic binary system consisting of a pulsating sdB star and a late F main-sequence companion (O'Donoghue et al. 1997), however the period and the orbit semi-major axes have not been precisely determined. This paper presents orbital characteristics of the EC 20117-4014 binary system using 20 years of photometric data. Periodic Observed minus Calculated (O-C) variations were detected in the two highest amplitude pulsations identified in the EC 20117-4014 power spectrum, indicating the binary system's precise orbital period (P = 792.3 days) and the light-travel time amplitude (A = 468.9 s). This binary shows no significant orbital eccentricity and the upper limit of the eccentricity is 0.025 (using 3 $\sigma$ as an upper limit). This upper limit of the eccentricity is the lowest among all wide sdB binaries with known orbital parameters. This analysis indicated that the sdB is likely to have lost its hydrogen envelope through stable Roche lobe overflow, thus supporting hypotheses for the origin of sdB stars. In addition to those results, the underlying pulsation period change obtained from the photometric data was $\dot{P}$ = 5.4 ($\pm$0.7) $\times$ $10^{-14}$ d d$^{-1}$, which shows that the sdB is just before the end of the core helium-burning phase

Galactic Structure Toward the Carina Tangent

This investigation presents a photometric study of the Galactic structure toward the Carina arm tangent. The field is located between 280 deg and 286 deg galactic longitude and -4 deg to 4 deg galactic latitude. All currently available uvbybeta data is used to obtain homogeneous color excesses and distances for more than 260 stars of spectral types O to G. We present revised distances and average extinction for the open clusters and cluster candidates NGC 3293, NGC 3114, Loden 46 and Loden 112. The cluster candidate Loden 112 appears to be a very compact group at a true distance modulus of 11.06 +\- 0.11 (s.e.) (1629 +84,-80 pc), significantly closer than previous estimates. We found other OB stars at that same distance and, based on their proper motions, suggest a new OB association at coordinates 282 deg < l < 285 deg, -2 deg < b < 2 deg. Utilizing BV photometry and spectral classification of the known O-type stars in the very young open cluster Wd 2 we provide a new distance estimate of 14.13 +\-0.16 (s.e.) (6698 +512,-475 pc), in excellent agreement with recent distance determinations to the giant molecular structures in this direction. We also discuss a possible connection between the HII region RCW 45 and the highly-reddened B+ star CPD -55 3036 and provide a revised distance for the luminous blue variable HR Car.Comment: accepted to PAS

First XMM-Newton observations of strongly magnetic cataclysmic variables - II. Timing studies of DP Leo and WW Hor

XMM-Newton was used to observe two eclipsing, magnetic cataclysmic variables, DP Leo and WW Hor, continuously for three orbital cycles each. Both systems were in an intermediate state of accretion. For WW Hor we also obtained optical light curves with the XMM-Newton Optical Monitor and from ground-based observations. Our analysis of the X-ray and optical light curves allows us to constrain physical and geometrical parameters of the accretion regions and derive orbital parameters and eclipse ephemerides of the systems. For WW Hor we directly measure horizontal and vertical temperature variations in the accretion column. From comparisons with previous observations we find that changes in the accretion spot longitude are correlated with the accretion rate. For DP Leo the shape of the hard X-ray light curve is not as expected for optically thin emission, showing the importance of optical depth effects in the post-shock region. We find that the spin period of the white dwarf is slightly shorter than the orbital period and that the orbital period is decreasing faster than expected for energy loss by gravitational radiation alone.Comment: Accepted for publication in MNRAS, 12 pages, 6 figure

A survey for pulsating subdwarf B stars with the Nordic Optical Telescope

A search programme for pulsating subdwarf B stars was conducted with the Nordic Optical Telescope on La Palma over 59 nights between 1999 and 2009. The purpose of the programme was to significantly extend the number of rapidly pulsating sdB stars to better understand the properties of this new group of variable compact stars. Candidates were selected initially from the HS and HE surveys, but were supplemented with additional objects from other surveys. Short sequences of time-series photometry were made on the candidates to determine the presence of rapid pulsations. In total twenty new pulsators were found in this survey, most of which have already been published and some extensively studied. We present four new short period pulsators, bringing the total of such pulsators up to 49. We also give limits on pulsation amplitudes for 285 objects with no obvious periodic variations, summarise the results of the survey, and provide improved physical parameters on the composite pulsators for which only preliminary estimates were published earlier.Comment: 17 pages, accepted for publication in A&

The rapidly pulsating sdO star, SDSS J160043.6+074802.9

A spectroscopic analysis of SDSS J160043.6+074802.9, a binary system containing a pulsating subdwarf-O (sdO) star with a late-type companion, yields Teff = 70 000 +/- 5000 K and log g = 5.25 +/- 0.30, together with a most likely type of K3V for the secondary star. We compare our results with atmospheric parameters derived by Fontaine et al. (2008) and in the context of existing evolution models for sdO stars. New and more extensive photometry is also presented which recovers most, but not all, frequencies found in an earlier paper. It therefore seems probable that some pulsation modes have variable amplitudes. A non-adiabatic pulsation analysis of uniform metallicity sdO models show those having log g > 5.3 to be more likely to be unstable and capable of driving pulsation in the observed frequency range.Comment: 14 pages, 12 figures, accepted for publication in MNRAS, 2009 September

The MultiSite Spectroscopic Telescope campaign: 2m spectroscopy of the V361 Hya variable PG1605+072

We present results and analysis for the 2m spectroscopic part of the MultiSite Spectroscopic Telescope (MSST) campaign undertaken in May/June 2002. The goal of the project was to observe the pulsating subdwarf B star PG1605+072 simultaneously in velocity and photometry and to resolve as many of the >50 known modes as possible, which will allow a detailed asteroseismological analysis. We have obtained over 150 hours of spectroscopy, leading to an unprecedented noise level of only 207m/s. We report here the detection of 20 frequencies in velocity, with two more likely just below our detection threshold. In particular, we detect 6 linear combinations, making PG1605+072 only the second star known to show such frequencies in velocity. We investigate the phases of these combinations and their parent modes and find relationships between them that cannot be easily understood based on current theory. These observations, when combined with our simultaneous photometry, should allow asteroseismology of this most complicated of sdB pulsators.Comment: 9 pages, 5 figures, accepted for publication in A&A; Figure 1 at lower resolution than accepted versio

Discovery of Five New R Coronae Borealis Stars in the MACHO Galactic Bulge Database

We have identified five new R Coronae Borealis (RCB) stars in the Galactic bulge using the MACHO Project photometry database, raising the total number of known Galactic RCB stars to about 40. We have obtained spectra to confirm the identifications. The fact that four out of the five newly identified RCB stars are ``cool'' (T(eff) 6000 K) suggests that the preponderance of warm RCB stars among the existing sample is a selection bias. These cool RCB stars are redder and fainter than their warm counterparts and may have been missed in surveys done with blue plates. Based on the number of new RCB stars discovered in the MACHO bulge fields, there may be ~250 RCB stars in the reddened "exclusion" zone toward the bulge.Comment: 16 pages, 5 figures, AJ in press High resolution versions of Figures 1 and 2 can be downloaded from http://morpheus.phys.lsu.edu/~gclayton/figs.pdf (more typos corrected