- ID:
- ivo://CDS.VizieR/J/AJ/137/3826
- Title:
- Two transits of the giant planet WASP-4b
- Short Name:
- J/AJ/137/3826
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present photometry of two transits of the giant planet WASP-4b with a photometric precision of 400-800 parts per million and a time sampling of 25-40s. The two midtransit times are determined to within 6s. Together with previously published times, the data are consistent with a constant orbital period, giving no compelling evidence for period variations that would be produced by a satellite or additional planets. Analysis of the new photometry, in combination with stellar-evolutionary modeling, gives a planetary mass and radius of 1.237+/-0.064M_Jup_ and 1.365+/-0.021R_Jup_, respectively. The planet is 15% larger than expected based on previously published models of solar-composition giant planets. With data of the quality presented here, the detection of transits of a "super-Earth" of radius 1.75R_{earth}_ would have been possible.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/761/162
- Title:
- Tycho-2 stars in Galactic Bulge Survey
- Short Name:
- J/ApJ/761/162
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We identify 69 X-ray sources discovered by the Galactic Bulge Survey (GBS) that are coincident with or very close to bright stars in the Tycho-2 catalog. Additionally, two other GBS sources are resolved binary companions to Tycho-2 stars where both components are separately detected in X-rays. Most of these are likely to be real matches, but we identify nine objects with large and significant X-ray-to-optical offsets as either detections of resolved binary companions or chance alignments. We collate known spectral types for these objects, and also examine Two Micron All Sky Survey colors, variability information from the All-Sky Automated Survey, and X-ray hardness ratios for the brightest objects. Nearly a third of the stars are found to be optically variable, divided roughly evenly between irregular variations and periodic modulations. All fall among the softest objects identified by the GBS. The sample forms a very mixed selection, ranging in spectral class from O9 to M3. In some cases, the X-ray emission appears consistent with normal coronal emission from late-type stars, or wind emission from early-types, but the sample also includes one known Algol, one W UMa system, two Be stars, and several X-ray bright objects likely to be coronally active stars or binaries. Surprisingly, a substantial fraction of the spectroscopically classified, non-coincidental sample (12 out of 38 objects) have late B or A type counterparts. Many of these exhibit redder near-IR colors than expected for their spectral type and/or variability, and it is likely that the X-rays originate from a late-type companion star in most or all of these objects.
1383. Tycho variables stars
- ID:
- ivo://CDS.VizieR/II/233
- Title:
- Tycho variables stars
- Short Name:
- II/233
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the classification procedure described in Piquard's PhD thesis applied to the 1091 stars presented in Piquard et al. (2001. Cat. <J/A+A/373/576>). In those six tables we give indication of variability type for all the stars detected as variables in Piquard et al. (2001, Cat. <J/A+A/373/576>). First of all, we looked for periodic signals in the light curves using adapted Renson's (Renson, 1978A&A....63..125R) and Stellingwerf's (Stellingwerf, 1978ApJ...224..953S) methods applied to the tree different photometric bands from Tycho (Cat. <I/239>): T, B_T_, V_T_ (the T band is defined from the added count-rates in the B_T_ and V_T_ channels, Grossmann et al.. 1995A&A...304..110G). Then we developed a semi-automatic method using 5 parameters (Period, color index, reduced proper motion from Tycho-2 catalogue (Cat. <I/259>), 2 indicators of the shape of the light curve) and a maximum likelihood method, combined with a careful look on the light curves. Finaly, the identification of the variability type is kept only if the resulting light curve is convincing (periodic the star has the P status, if not periodic the star has the U status); else we need more information about the star and is has the A status. All this identifications are indications since the quality of the light curves are often poor, particularly when the star is fainter than T=10.
- ID:
- ivo://CDS.VizieR/J/AcA/58/293
- Title:
- Type-II and anomalous Cepheids in LMC
- Short Name:
- J/AcA/58/293
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the second part of the OGLE-III Catalog of Variable Stars (OIII-CVS) we present 197 type II Cepheids and 83 anomalous Cepheids in the Large Magellanic Cloud (LMC). The sample of type II Cepheids consists of 64 BL Her stars, 96 W Vir stars and 37 RV Tau stars. Anomalous Cepheids are divided into 62 fundamental-mode and 21 first-overtone pulsators. These are the largest samples of such types of variable stars detected anywhere outside the Galaxy.
- ID:
- ivo://CDS.VizieR/J/A+A/603/A70
- Title:
- Type II and anomalous Cepheids luminosities
- Short Name:
- J/A+A/603/A70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Type II and anomalous Cepheids (ACs) are useful distance indicators when there are too few classical Cepheids or when RR Lyrae stars are too faint. Type II and ACs follow a period-luminosity relation as well, but they are less well-studied classes of objects. In this paper we study the sample of 335 Type II and ACs in the Small and Large Magellanic Clouds detected in OGLE-III data. The spectral energy distributions (SEDs) are constructed from photometric data available in the literature and fitted with a dust radiative transfer model, thereby leading to a determination of luminosity and effective temperature. In addition, a subsample of targets is investigated for possible binarity by looking for the light-time travel effect (LITE). Hertzsprung-Russell diagrams (HRD) are constructed and compared to evolutionary tracks and theoretical instability strips (ISs). In agreement with previous suggestions, the BL Her subclass can be explained by the evolution of ~0.5-0.6M_{sun}_ stars evolving off the zero-age horizontal branch and the ACs can be explained by the evolution of ~1.1-2.3M_{sun}_ stars. The evolution of the W Vir subclass is not clear. These objects are at higher luminosities than ACs and evolutionary tracks of ~2.5-4M_{sun}_ stars cross this region in the HRD, but the periods of the W Vir are longer than those of the short period classical Cepheids at these luminosities, which indicates the former have lower masses. A low-mass star experiencing a thermal pulse when the envelope mass is small can make a blue loop into the IS region of the W Vir stars. But the timescale is extremely short, so this is also no explanation for the W Vir as a class. A relation to binarity might be at the origin of the W Vir stars, which has already been explicitly suggested for the peculiar W Vir stars. For ~60% of the RV Tau and ~10% of the W Vir objects an infrared excess is detected from the SED fitting. A recent result is confirmed that stars exist with luminosities below that predicted from single-star evolution, which show a clear infrared excess, and the shape of the excess suggests a connection to binary evolution. The investigation of the LITE effect revealed 20 systems that appear to show periodic variations and may be new binaries, although this study requires follow-up. About 40 stars show significant period changes.
- ID:
- ivo://CDS.VizieR/J/MNRAS/386/2115
- Title:
- Type II Cepheid and RR Lyrae variables
- Short Name:
- J/MNRAS/386/2115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Infrared and optical absolute magnitudes are derived for the type II Cepheids kappa Pav and VY Pyx using revised Hipparcos parallaxes and for kappa Pav, V553 Cen and SW Tau from pulsational parallaxes. Revised Hipparcos and HST parallaxes for RR Lyrae agree satisfactorily and are combined in deriving absolute magnitudes. Phase-corrected J, H and Ks mags are given for 142 Hipparcos RR Lyraes based on Two-Micron All-Sky Survey observations. Pulsation and trigonometrical parallaxes for classical Cepheids are compared to establish the best value for the projection factor (p) used in pulsational analyses.
- ID:
- ivo://CDS.VizieR/J/AJ/146/61
- Title:
- Type II Cepheid candidates. IV. Objects from NSVS
- Short Name:
- J/AJ/146/61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained VR photometry of 447 Cepheid variable star candidates with declinations north of -14{deg}30', most of which were identified using the Northern Sky Variability Survey (NSVS) data archive. Periods and other photometric properties were derived from the combination of our data with the NSVS data. Atmospheric parameters were determined for 81 of these stars from low-resolution spectra. The identification of type II Cepheids based on the data presented in all four papers in this series is discussed. On the basis of spectra, 30 type II Cepheids were identified while 53 variables were identified as cool, main sequence stars and 283 as red giants following the definitions in Paper III. An additional 30 type II Cepheids were identified on the basis of light curves. The present classifications are compared with those from the Machine-learned All Sky Automated Survey Classification Catalog for 174 stars in common.
1388. Type II Cepheids
- ID:
- ivo://CDS.VizieR/J/AJ/114/341
- Title:
- Type II Cepheids
- Short Name:
- J/AJ/114/341
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have determined the photospheric compositions of five luminous F-G variables in globular clusters: V11 in M2, V42 in M5, V84 in M5, V2 in M10, and V17 in M28, three of which are classified as RV Tau variable stars. Unlike the recent findings that the photospheres of field RV Tau variables have been altered by a gas-dust separation process, none of these stars, except possibly V2 in M10, show such signs. We suggest that either a smaller carbon abundance in the photosphere of a globular cluster RV Tau star (compared to its field analogues) might be a factor in the gas-dust separation process due to the lack of sufficient carbon grain formation, or the stellar winds and their efficacy as dust-grain separators is influenced by the metallicity of the stellar envelope which, unlike the photosphere, is never subject to alteration by a dust-gas separation. Our analysis is most complete for V84, for which we have estimated the abundances of 19 chemical elements. Compared to the other giants in M5, this star displays a very large excess of Na and a deficit of O. This finding is consistent with a recently proposed mechanism of Na production in the ON-cycling region of metal-poor RGB stars. The value of [Al/Fe] for V84 is also high (also consistent with ON-cycling), but a comparison with the other cluster giants cannot be performed until Al is measured in their spectra. The s-process elements are not significantly enhanced in the atmosphere of V84 relative to the other cluster members. (c) 1997 American Astronomical Society.
- ID:
- ivo://CDS.VizieR/J/MNRAS/477/2276
- Title:
- Type II Cepheids abundances
- Short Name:
- J/MNRAS/477/2276
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The chemical composition of 28 Population II Cepheids and one RR Lyrae variable has been studied using high-resolution spectra. The chemical composition of W Vir variable stars (with periods longer than 8 d) is typical for the halo and thick disc stars. However, the chemical composition of BL Her variables (with periods of 0.8-4 d) is drastically different, although it does not differ essentially from that of the stars belonging to globular clusters. In particular, the sodium overabundance ([Na/Fe]~=0.4) is reported for most of these stars, and the Na-O anticorrelation is also possible. The evolutionary tracks for BL Her variables (with a progenitor mass value of 0.8 solar masses) indicate that mostly helium-overabundant stars (Y=0.30-0.35) can fall into the instability strip region. We suppose that it is the helium overabundance that accounts not only for the existence of BL Her variable stars but also for the observed abnormalities in the chemical composition of this small group of pulsating variables.
- ID:
- ivo://CDS.VizieR/J/A+A/619/A51
- Title:
- Type II Cepheids in the Galactic bulge
- Short Name:
- J/A+A/619/A51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new Near-Infrared photometry of Type II Cepheids in the Bulge from the VISTA Variables in the Via Lactea survey (VVV) (Minniti et al., 2010NewA...15..433M; Saito et al., 2012A&A...537A.107S, Cat. II/337. We provide the largest sample (894 stars) of T2Cs with JHKs observations that have accurate periods from the OGLE catalog (Soszynski et al., 2017, Cat. J/AcA/67/297). Our analysis makes use of the Ks-band time-series observations to estimate mean-magnitudes and individual distances by means of the Period-Luminosity PL relation. To constrain the kinematic properties of our targets, we complement our analysis with proper motions based on both the VVV and Gaia Data Release 2.
