- 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.
Number of results to display per page
Search Results
- 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.
- ID:
- ivo://CDS.VizieR/J/AJ/118/2211
- Title:
- M31F eclipsing binaries and Cepheids
- Short Name:
- J/AJ/118/2211
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As a first step in the DIRECT project, between September 1996 and October 1997 we obtained 95 full/partial nights on the F.L. Whipple Observatory 1.2m 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 fifth in the series, we present the catalog of variable stars found in the field M31F [(RA, DE) = (10.10{deg}, 40.72{deg}), J2000.0]. We have found 64 variable stars: four eclipsing binaries, 52 Cepheids and eight 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/MNRAS/337/519
- Title:
- M giants in MACHO, DENIS and ISOGAL
- Short Name:
- J/MNRAS/337/519
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A 'complete' sample of 174 M giants classified in the mid-1980s by Blanco (1986AJ.....91..290B) and later than subtype M0 in the NGC 6522 Baade's Window clear field has been investigated to establish some general properties of cool bulge stars. Photometric information has been obtained from the MACHO data base to search for variability and, where possible, to determine periods. Near- and mid-infrared magnitudes have been extracted from DENIS (<B/denis>) and ISOGAL (<II/243>). 46 semiregular variables (SRVs) and two irregular variables were found amongst the 174. Many M5 and all stars M6 or later show variation, whereas earlier subtypes (M1-M4) do not.
- ID:
- ivo://CDS.VizieR/J/AJ/134/1488
- Title:
- MG1 Variable Star Catalog (MG1-VSC)
- Short Name:
- J/AJ/134/1488
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the first MOTESS-GNAT variable-star survey, a deep, wide-field variability survey conducted over 2yr with a total sky coverage of 300deg^2^. In this survey, we identified 26042 variable-star candidates with magnitudes R=13-19, including 5271 that are periodic at the 99% confidence level. We recovered 59 out of 68 members of the General Catalogue of Variable Stars (GCVS) that are in this brightness range. We discuss the implications for completeness and accuracy for both this survey and the GCVS; the implied completeness for distinctly classifiable variable stars in our survey is ~85%-90%. We also discuss some of the caveats of our survey results. We conclude that this instrument design is ideal for an inexpensive, longitudinally distributed telescope network that could be used to study faint or rare transient phenomena in a previously unexplored regime of parameter space.
- ID:
- ivo://CDS.VizieR/J/A+A/530/A120
- Title:
- Mid-infrared diameter of W Hya
- Short Name:
- J/A+A/530/A120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Mid-infrared (N-band) interferometric data of W Hya were obtained with MIDI/VLTI between April 2007 and September 2009, covering nearly three pulsation cycles. The spectrally dispersed visibility data of all 75 observations were analyzed by fitting a circular fully limb-darkened disk (FDD) model to all data and individual pulsation phases. Asymmetries were studied with an elliptical FDD. Modeling results in an apparent angular FDD diameter of W Hya of about (80+/-1.2)mas (7.8AU) between 8 and 10 micron, which corresponds to an about 1.9 times larger diameter than the photospheric one. The diameter gradually increases up to (105+/-1.2)mas (10.3AU) at 12 micron. In contrast, the FDD relative flux fraction decreases from (0.85+/-0.02) to (0.77+/-0.02), reflecting the increased flux contribution from a fully resolved surrounding silicate dust shell. The asymmetric character of the extended structure could be confirmed. An elliptical FDD yields a position angle of (11+/-20)deg and an axis ratio of (0.87+/-0.07). A weak pulsation dependency is revealed with a diameter increase of (5.4+/-1.8)mas between visual minimum and maximum, while detected cycle-to-cycle variations are smaller.
- ID:
- ivo://CDS.VizieR/J/MNRAS/441/715
- Title:
- Mid-infrared study of RR Lyrae stars
- Short Name:
- J/MNRAS/441/715
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a group of 3740 previously identified RR Lyrae variables well observed with the Wide-field Infrared Survey Explorer (WISE). We explore how the shape of the generic RR Lyrae mid-infrared light curve varies over period-space, comparing light curves in mid-infrared and optical bands. We find that optical light curves exhibit high amplitudes and a large spectrum of light-curve shapes, while mid-infrared light curves have low amplitudes and uniform light-curve shapes. From the period-space analysis, we hope to improve the classification methods of RR Lyrae variables and enable reliable discovery of these pulsators in the WISE catalogue and future mid-infrared surveys such as the James Webb Space Telescope. We provide mid-infrared templates for typical RR Lyrae stars and demonstrate how these templates can be applied to improve estimates of mid-infrared RR Lyrae mean magnitude, which is used for distance measurement. This method of template fitting is particularly beneficial for improving observational efficiency. For example, using light curves with observational noise of 0.05mag, we obtain the same level of accuracy in mean magnitude estimates for light curves randomly sampled at 12 data points with template fitting as with light curves randomly sampled at 20 data points with harmonic modelling.
- ID:
- ivo://CDS.VizieR/J/ApJ/679/71
- Title:
- Mid-IR period-luminosity relations
- Short Name:
- J/ApJ/679/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first mid-infrared period-luminosity (PL) relations for Large Magellanic Cloud (LMC) Cepheids. Single-epoch observations of 70 Cepheids were extracted from Spitzer IRAC observations at 3.6, 4.5, 5.8 and 8.0um, serendipitously obtained during the SAGE (Surveying the Agents of a Galaxy's Evolution) imaging survey of the LMC. All four mid-infrared PL relations have nearly identical slopes over the period range 6-88 days, with a small scatter of only +/-0.16mag independent of period for all four of these wavelengths. We emphasize that differential reddening is not contributing significantly to the observed scatter, given the nearly 2 orders of magnitude reduced sensitivity of the mid-IR to extinction compared to the optical. Future observations, filling in the light curves for these Cepheids, should noticeably reduce the residual scatter. These attributes alone suggest that mid-infrared PL relations will provide a practical means of significantly improving the accuracy of Cepheid distances to nearby galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/733/50
- Title:
- Mid-IR photometric monitoring of the ONC
- Short Name:
- J/ApJ/733/50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present initial results from time-series imaging at infrared wavelengths of 0.9deg^2^ in the Orion Nebula Cluster (ONC). During Fall 2009 we obtained 81 epochs of Spitzer 3.6 and 4.5um data over 40 consecutive days. We extracted light curves with ~3% photometric accuracy for ~2000 ONC members ranging from several solar masses down to well below the hydrogen-burning mass limit. For many of the stars, we also have time-series photometry obtained at optical (Ic) and/or near-infrared (JKs) wavelengths. Our data set can be mined to determine stellar rotation periods, identify new pre-main-sequence eclipsing binaries, search for new substellar Orion members, and help better determine the frequency of circumstellar disks as a function of stellar mass in the ONC. Our primary focus is the unique ability of 3.6 and 4.5um variability information to improve our understanding of inner disk processes and structure in the Class I and II young stellar objects (YSOs). In this paper, we provide a brief overview of the YSOVAR Orion data obtained in Fall 2009 and highlight our light curves for AA-Tau analogs -YSOs with narrow dips in flux, most probably due to disk density structures passing through our line of sight. Detailed follow-up observations are needed in order to better quantify the nature of the obscuring bodies and what this implies for the structure of the inner disks of YSOs.
