- ID:
- ivo://CDS.VizieR/J/A+A/618/A15
- Title:
- Parameters of EHB stars in {omega} Cen
- Short Name:
- J/A+A/618/A15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The presence of extreme horizontal branch (EHB) and blue hook stars in some Galactic globular clusters (GGCs) constitutes one of the remaining mysteries of stellar evolution. While several evolutionary scenarios have been proposed to explain the characteristics of this peculiar population of evolved stars, their observational verification has been limited by the availability of spectroscopic data for a statistically significant sample of such objects in any single GGC. In this first paper, we focus on {omega} Centauri, a peculiar, massive GGC that hosts multiple stellar populations. We use non-LTE model atmospheres to derive atmospheric parameters (Teff, log g and N(He)/N(H)) and spectroscopic masses for 152 EHB stars in the cluster. We also search for close binaries among these stars based on radial velocity variations. The majority of our sample consists of sdOB stars that have roughly solar or super-solar atmospheric helium abundances. It is these objects that constitute the blue hook at V>18.5mag in the {omega} Cen colour-magnitude diagram.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/547/A109
- Title:
- Parameters of HB stars in {omega} Cen
- Short Name:
- J/A+A/547/A109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the reddening, surface helium abundance and spectroscopic mass of 115 blue horizontal branch (HB) and blue hook (BH) stars in {omega} Centauri (NGC5139), spanning the cluster HB from the blue edge of the instability strip (T_eff_=8000K) to BH objects with T_eff_~50000K.
- ID:
- ivo://CDS.VizieR/J/ApJ/805/94
- Title:
- Periodicities in KIC 3527751 from 3yr Kepler data
- Short Name:
- J/ApJ/805/94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze 3yr of nearly continuous Kepler spacecraft short cadence observations of the pulsating subdwarf B (sdB) star KIC 3527751. We detect a total of 251 periodicities, most in the g-mode domain, but some where p-modes occur, confirming that KIC3527751 is a hybrid pulsator. We apply seismic tools to the periodicities to characterize the properties of KIC3527751. Techniques to identify modes include asymptotic period spacing relationships, frequency multiplets, and the separation of multiplet splittings. These techniques allow for 189 (75%) of the 251 periods to be associated with pulsation modes. Included in these are three sets of l=4 multiplets and possibly an l=9 multiplet. Period spacing sequences indicate l=1 and 2 overtone spacings of 266.4+/-0.2 and 153.2+/-0.2s, respectively. We also calculate reduced periods, from which we find evidence of trapped pulsations. Such mode trappings can be used to constrain the core/atmosphere transition layers. Interestingly, frequency multiplets in the g-mode region, which sample deep into the star, indicate a rotation period of 42.6+/-3.4days while p-mode multiplets, which sample the outer envelope, indicate a rotation period of 15.3+/-0.7days. We interpret this as differential rotation in the radial direction with the core rotating more slowly. This is the first example of differential rotation for a sdB star.
- ID:
- ivo://CDS.VizieR/J/A+A/638/A108
- Title:
- 4 p-mode pulsators arrival times
- Short Name:
- J/A+A/638/A108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate variations in the arrival time of coherent stellar pulsations due to the light travel time effect to test for the presence of sub-stellar companions. Those companions are the key to one possible formation scenario of apparently single subdwarf B stars. We make use of an extensive set of ground-based observations of the four large amplitude p-mode pulsators DW Lyn, V1636 Ori, QQ Vir and V541 Hya. Observations of the TESS space telescope are available on two of the targets. The timing method compares the phase of sinusoidal fits to the full multi-epoch ligh curves with phases from the fit of a number of subsets of the original time series. TESS observations do not sample the pulsations well enough to be useful due to the (currently) fixed 2 minute cadence. From the ground- based observations, we infer evolutionary parameters from the arrival times. The residual signals show many statistically significant periodic signals, but no clear evidence for changes in arrival time induced by sub-stellar companions. The signals can be explained partly by mode beating effects. We derive upper limits on companion masses set by the observational campaign.
- ID:
- ivo://CDS.VizieR/J/A+A/530/A28
- Title:
- Priority targets for the MUCHFUSS project
- Short Name:
- J/A+A/530/A28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims at finding sdBs with compact companions like supermassive white dwarfs (M>1.0M_{sun}_), neutron stars or black holes. The existence of such systems is predicted by binary evolution theory and recent discoveries indicate that they are likely to exist in our Galaxy. A determination of the orbital parameters is sufficient to put a lower limit on the companion mass by calculating the binary mass function. If this lower limit exceeds the Chandrasekhar mass and no sign of a companion is visible in the spectra, the existence of a massive compact companion is proven without the need for any additional assumptions. We identified about 1100 hot subdwarf stars from the SDSS by colour selection and visual inspection of their spectra. Stars with high velocities have been reobserved and individual SDSS spectra have been analysed. In total 127 radial velocity variable subdwarfs have been discovered. Binaries with high RV shifts and binaries with moderate shifts within short timespans have the highest probability of hosting massive compact companions. Atmospheric parameters of 69 hot subdwarfs in these binary systems have been determined by means of a quantitative spectral analysis. The atmospheric parameter distribution of the selected sample does not differ from previously studied samples of hot subdwarfs. The systems are considered the best candidates to search for massive compact companions by follow-up time resolved spectroscopy.
- ID:
- ivo://CDS.VizieR/J/PASP/109/849
- Title:
- Probing the LHS Catalog
- Short Name:
- J/PASP/109/849
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present moderate resolution spectroscopy of 111 cool dwarf stars to supplement the observations we have already presented in the Palomar/MSU Nearby-Star Spectroscopic Survey. The sample consists of 71 suspected nearby stars added to the Preliminary Third Catalog of Nearby Stars since 1991 as well as 40 faint red stars selected from the LHS catalog. The study was aimed at identifying interesting red dwarfs, particularly new nearby, ultracool dwarfs, and very metal-poor stars. The observations were made using the Palomar 60-inch, the Hale 200-inch and the Las Campanas 100-inch telescopes between June 1995 and January 1996. The spectral resolution is approximately 3 Angstroms per pixel with wavelength coverage from 6200 to 7500 Angstroms. Table 2 contains bandstrengths for TiO, CaH, and CaOH indices.
- ID:
- ivo://CDS.VizieR/III/144
- Title:
- Radial Velocities for High Proper Motion Stars
- Short Name:
- III/144
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The machine-readable version of Radial Velocities of High Proper Motion Stars contains UBV photometry, proper motions, and radial (line-of-sight) velocities for 878 high-proper-motion stars that were selected from the subdwarf candidate list of Sandage and Fouts (1986).
- ID:
- ivo://CDS.VizieR/J/A+A/450/1149
- Title:
- Radial velocity curve of Balloon 090100001
- Short Name:
- J/A+A/450/1149
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained 2552 useful low-resolution spectra of the bright sdBV Balloon 090100001, which form the first large time-resolved spectroscopic dataset of this brightest known pulsating subdwarf B star. The data were obtained at the Nordic Optical Telescope during 7 nights in August/September 2004 over a total time base of 38 nights, aiming to derive pulsational characteristics of this star. In this paper we present the observations and the results obtained from frequency analyses. In our data we find clear evidence for 8 independent frequencies, that were all previously reported in photometric monitoring studies, allowing future asteroseismological studies of this star to be constrained by combined photometric and spectroscopic observations of as much as 8 pulsation modes. We do not find conclusive evidence for new frequencies. We present the first determination of the pulsational radial-velocity amplitudes of this star, and find that the radial-velocity amplitude of the main pulsation mode (f_1_=2.80749mHz) in Balloon 090100001 is 18.9km/s, which is the largest radial-velocity amplitude found in sdB-star pulsations so far.
- ID:
- ivo://CDS.VizieR/J/MNRAS/421/2798
- Title:
- Radial velocity monitoring of PG 1018-047
- Short Name:
- J/MNRAS/421/2798
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- About 50 per cent of all known hot subdwarf B stars (sdBs) reside in close (short-period) binaries, for which common-envelope ejection is the most likely formation mechanism. However, Han et al. (2002MNRAS.336..449H, 2003MNRAS.341..669H) predict that the majority of sdBs should form through stable mass transfer leading to long-period binaries. Determining orbital periods for these systems is challenging and while the orbital periods of ~100 short-period systems have been measured, there are no periods measured above 30d. As part of a large programme to characterize the orbital periods of sdB binaries and their formation history, we have found that PG 1018-047 has an orbital period of 759.8+/-5.8d, easily making it the longest period ever detected for a sdB binary. Exploiting the Balmer lines of the subdwarf primary and the narrow absorption lines of the companion present in the spectra, we derive the radial velocity amplitudes of both stars, and estimate the mass ratio M_MS_/M_sdB_=1.6+/-0.2. From the combination of visual and infrared photometry, the spectral type of the companion star is determined to be mid-K.
- ID:
- ivo://CDS.VizieR/J/A+A/442/1023
- Title:
- Radial velocity of 17 bright subdwarf B stars
- Short Name:
- J/A+A/442/1023
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Radial velocity curves for 15 bright subdwarf B binary systems have been measured using high precision radial velocity measurements from high S/N optical high-resolution spectra. In addition, two bright sdB stars are discovered to be radial velocity variable but the period could not yet be determined. The companions for all systems are unseen.
