- ID:
- ivo://CDS.VizieR/J/A+A/604/A29
- Title:
- MC Type II and anomalous Cepheids PL and PR
- Short Name:
- J/A+A/604/A29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Type II Cepheids (T2Cs) and anomalous Cepheids (ACs) are pulsating stars that follow separate period-luminosity relations. We study the period-luminosity (PL) and period-radius (PR) relations for T2Cs and ACs in the Magellanic Clouds. In an accompanying paper we determined luminosity and effective temperature for the 335 T2Cs and ACs in the LMC and SMC discovered in the OGLE-III survey, by constructing the spectral energy distribution (SED) and fitting this with model atmospheres and a dust radiative transfer model (in the case of dust excess). Building on these results we study the PL- and PR relations. Using existing pulsation models for RR Lyrae and classical Cepheids we derive the period-luminosity-mass-temperature-metallicity relations, and then estimate the pulsation mass.
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- ID:
- ivo://CDS.VizieR/J/AJ/118/346
- Title:
- M31D eclipsing binaries and Cepheids
- Short Name:
- J/AJ/118/346
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We undertook a long-term project, DIRECT, to obtain the direct distances to two important galaxies in the cosmological distance ladder - M31 and M33 - using detached eclipsing binaries (DEBs) and Cepheids. While rare and difficult to detect, DEBs provide us with the potential to determine these distances with an accuracy better than 5%. The extensive photometry obtained in order to detect DEBs provides us with good light curves for the Cepheid variables. These are essential to the parallel project to derive direct Baade-Wesselink distances to Cepheids in M31 and M33. For both Cepheids and eclipsing binaries, the distance estimates will be free of any intermediate steps. As a first step in the DIRECT project, between 1996 September and 1997 October we obtained 95 full/partial nights on the F. L. Whipple Observatory 1.2 m telescope and 36 full nights on the Michigan-Dartmouth-MIT 1.3 m telescope to search for DEBs and new Cepheids in the M31 and M33 galaxies. In this paper, the fourth in the series, we present the catalog of variable stars, most of them newly detected, found in the field M31D [(RA, DE)=(11.03{deg}, 41.27{deg}), J2000.0]. We have found 71 variable stars: five eclipsing binaries, 38 Cepheids, and 28 other periodic, possible long-period or nonperiodic variables. The catalog of variables, as well as their photometry and finding charts, is available via anonymous ftp and the World Wide Web. The complete set of the CCD frames is available upon request.
- ID:
- ivo://CDS.VizieR/J/ApJS/173/673
- Title:
- M dwarf UV flares in GALEX
- Short Name:
- J/ApJS/173/673
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the preliminary results from implementing a new software tool that enables inspection of time-tagged photon data for the astronomical sources contained within individual GALEX ultraviolet (UV) images of the sky. We have inspected the photon data contained within 1802 GALEX images to reveal rapid, short-term (<~500s) UV source variability in the form of stellar "flares." The mean associated change in near-UV (NUV) magnitude due to this flaring activity is 2.7+/-0.3mag. A list of 49 new UV variable star candidates is presented (associated with 52 separate flare events), together with their associated Sloan Digital Sky Survey (SDSS) photometric magnitudes. From these data we can associate the main source of these UV flare events with magnetic activity on M dwarf stars. Photometric parallaxes have been determined for 32 of these sources, placing them at distances ranging from approximately 25 to 1000pc. The average UV flare energy for these flare events is 2.5x10^30^ergs, which is of a similar energy to that of U-band, X-ray, and EUV flares observed on many local M dwarf stars. We have found that stars of classes M0 to M5 flare with energies spanning a far larger range and with an energy approximately 5 times greater than those of later (M6 to M8) spectral type.
- ID:
- ivo://CDS.VizieR/J/A+A/393/167
- Title:
- Mean Spectra for upper AGB stars
- Short Name:
- J/A+A/393/167
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Provided are average spectra extending from 510 to 2490nm for: - Oxygen rich, optically visible LPVs (temperature sequence based on the colour I-K); - Carbon rich, optically visible LPVs (temperature sequence based on the colour R-H, and C/O sequence); - Oxygen rich, dust-enshrouded LPVs (reddened versions of the coolest optically visible average); - Carbon rich, dust-enshrouded LPVs (reddened versions of the coolest optically visible average).
- ID:
- ivo://CDS.VizieR/J/A+A/421/937
- Title:
- Metal abundances of LMC RR Lyrae
- Short Name:
- J/A+A/421/937
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Metallicities ([Fe/H]) from low resolution spectroscopy obtained with the Very Large Telescope (VLT) are presented for 98 RR Lyrae and 3 short period Cepheids in the bar of the Large Magellanic Cloud. Our metal abundances have typical errors of +/-0.17dex. The average metallicity of the RR Lyrae stars is [Fe/H]=-1.48+/-0.03+/-0.06 on the scale of Harris (1996, Cat. <VII/202>). The star-to-star scatter (0.29dex) is larger than the observational errors, indicating a real spread in metal abundances. The derived metallicities cover the range -2.12<[Fe/H]<-0.27, but there are only a few stars having [Fe/H]>-1. For the ab-type variables we compared our spectroscopic abundances with those obtained from the Fourier decomposition of the light curves. We find good agreement between the two techniques, once the systematic offset of 0.2 dex between the metallicity scales used in the two methods is taken into account. The spectroscopic metallicities were combined with the dereddened apparent magnitudes of the variables to derive the slope of the luminosity-metallicity relation for the LMC RR Lyrae stars: the resulting value is 0.214+/-0.047mag/dex. Finally, the 3 short period Cepheids have [Fe/H] values in the range -2.0<[Fe/H]<-1.5. They are more metal-poor than typical LMC RR Lyrae stars, thus they are more likely to be Anomalous Cepheids rather than the short period Classical Cepheids that are often found in a number of dwarf Irregular galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/640/L43
- Title:
- Metallicities of RR Lyrae stars in Omega Cen
- Short Name:
- J/ApJ/640/L43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new spectroscopic metal abundances for 74 RR Lyrae (RRL) stars in {omega} Cen obtained with FLAMES. The well-known metallicity spread is visible among the RRL variables. The metal-intermediate (MI) RRL stars ([Fe/H]~-1.2) are fainter than the bulk of the dominant metal-poor population ([Fe/H]~-1.7), in good agreement with the corresponding zero-age horizontal-branch models with cosmological helium abundance Y=0.246.
- ID:
- ivo://CDS.VizieR/J/AJ/136/2441
- Title:
- Metallicity of RR0 Lyrae in the galactic bulge
- Short Name:
- J/AJ/136/2441
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present metallicities of 2690 RR0 Lyrae stars observed toward the MACHO Survey fields in the Galactic bulge. These [Fe/H] values are based upon an empirically-calibrated relationship that uses the Fourier coefficients of the light curve and are accurate to +/-0.2dex. The majority of the RR0 Lyrae stars in our sample are located in the Galactic bulge, but 255 RR0 stars are associated with the Sagittarius (Sgr) dwarf galaxy.
- ID:
- ivo://CDS.VizieR/J/A+A/308/481
- Title:
- Metallic line doubling phenomenon in RR Lyrae
- Short Name:
- J/A+A/308/481
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- For the first time, the observation of the line doubling phenomenon over two metallic absorption lines of a RR Lyrae star (RR Lyr) is reported. A resolving power of 42,000 and a time resolution close to 1% of the pulsating period were necessary. Although a smaller exposure time would be required to completely resolve this phenomenon over the whole spectrum, we interpret it as the consequence of a "two-step" Schwarzschild's mechanism. Thus a strong shock wave propagating throughout the photosphere around phase 0.93 would be at the origin of the observed line doubling. Because the shock undergoes a sudden acceleration phase, a "jump" appears in the line profile evolution. The shock is first receding and then almost stationary. Our qualitative interpretation needs a theoretical confirmation with the help of a nonlinear nonadiabatic pulsational model with an extended atmosphere taking into account the presence of shock waves. Nevertheless it appears from our observations that the dynamics of the atmosphere of RR Lyr is important just above the photosphere and that strong shock exists at this level because the doubling is already present in FeI lines.
- ID:
- ivo://CDS.VizieR/J/AJ/155/45
- Title:
- Metal-rich RRc stars in the Carnegie RR Lyrae Survey
- Short Name:
- J/AJ/155/45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe and employ a stacking procedure to investigate abundances derived from the low signal-to-noise ratio spectra obtained in the Carnegie RR Lyrae Survey (CARRS). We find iron metallicities that extend from [Fe/H]~-2.5 to values at least as large as [Fe/H]~-0.5 in the 274-spectrum CARRS RRc data set. We consider RRc sample contamination by high amplitude solar metallicity {delta} Scuti stars (HADS) at periods less than 0.3 days, where photometric discrimination between RRc and {delta} Scuti stars has proven to be problematic. We offer a spectroscopic discriminant, the well-marked overabundance of heavy elements, principally [Ba/H], that is a common, if not universal, characteristic of HADS of all periods and axial rotations. No bona fide RRc stars known to us have verified heavy-element overabundances. Three out of 34 stars in our sample with [Fe/H]>-0.7 exhibit anomalously strong features of Sr, Y, Zr, Ba, and many rare earths. However, carbon is not enhanced in these three stars, and we conclude that their elevated n-capture abundances have not been generated in interior neutron-capture nucleosynthesis. Contamination by HADS appears to be unimportant, and metal-rich RRc stars occur in approximately the same proportion in the Galactic field as do metal-rich RRab stars. An apparent dearth of metal-rich RRc is probably a statistical fluke. Finally, we show that RRc stars have a similar inverse period-metallicity relationship as has been found for RRab stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/466/1290
- Title:
- Metal-rich SX Phe stars in Kepler field
- Short Name:
- J/MNRAS/466/1290
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A spectroscopic and photometric analysis has been carried out for 32 candidate SX Phe variable blue straggler stars in the Kepler field. Radial velocities (RVs), space motions (U, V, W), projected rotation velocities (vsini), spectral types and atmospheric characteristics (T_eff_, logg, [Fe/H], {xi}_t_, {zeta}_RT_, etc.) are presented for 30 of the 32 stars. Although several stars are metal-weak with extreme halo orbits, the mean [Fe/H] of the sample is near-solar, thus the stars are more metal-rich than expected for a typical sample of Pop. II stars and more like halo metal-rich A-type stars. Two-thirds of the stars are fast rotators with vsini>50km/s^, including four stars with vsini>200km/s. Three of the stars have (negative) RVs>250km/s^, five have retrograde space motions and 21 have total speeds (relative to the Local Standard of Rest) >400km/s. All but one of the 30 stars have positions in a Toomre diagram consistent with the kinematics of bona fide halo stars (the exception being a thick-disc star). Observed Romer time delays, pulsation frequency modulations and light curves suggest that at least one-third of the stars are in binary (or triple) systems with orbital periods ranging from 2.3d to more than four years.
