- ID:
- ivo://CDS.VizieR/J/MNRAS/446/4008
- Title:
- RT Aur and SZ tau UBV light curves
- Short Name:
- J/MNRAS/446/4008
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The quantity and quality of satellite photometric data strings is revealing details in Cepheid variation at very low levels. Specifically, we observed a Cepheid pulsating in the fundamental mode and one pulsating in the first overtone with the Canadian MOST (Microvariability and Oscillations of Stars) satellite. The 3.7-d period fundamental mode pulsator (RT Aur) has a light curve that repeats precisely, and can be modelled by a Fourier series very accurately. The overtone pulsator (SZ Tau, 3.1d period) on the other hand shows light-curve variation from cycle to cycle which we characterize by the variations in the Fourier parameters. We present arguments that we are seeing instability in the pulsation cycle of the overtone pulsator, and that this is also a characteristic of the O-C curves of overtone pulsators. On the other hand, deviations from cycle to cycle as a function of pulsation phase follow a similar pattern in both stars, increasing after minimum radius. In summary, pulsation in the overtone pulsator is less stable than that of the fundamental mode pulsator at both long and short time-scales.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/156/147
- Title:
- RV and activity measurements of Kepler-1656
- Short Name:
- J/AJ/156/147
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Kepler-1656b is a 5 R_{Earth}_ planet with an orbital period of 32 days initially detected by the prime Kepler mission. We obtained precision radial velocities of Kepler-1656 with Keck/HIRES in order to confirm the planet and to characterize its mass and orbital eccentricity. With a mass of 48+/-4 M_{Earth}_, Kepler-1656b is more massive than most planets of comparable size. Its high mass implies that a significant fraction, roughly 80%, of the planet's total mass is in high-density material such as rock/iron, with the remaining mass in a low-density H/He envelope. The planet also has a high eccentricity of 0.84+/-0.01, the largest measured eccentricity for any planet less than 100 M_{Earth}_. The planet's high density and high eccentricity may be the result of one or more scattering and merger events during or after the dispersal of the protoplanetary disk.
- ID:
- ivo://CDS.VizieR/J/A+A/499/935
- Title:
- RV curves of 42 Dra and HD 139357
- Short Name:
- J/A+A/499/935
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- For the past 3 years we have been monitoring 62 K giant stars using precise stellar radial velocity (RV) measurements with the 2m Alfred Jensch Telescope of the Thuringer Landessternwarte Tautenburg (TLS). To probe the dependence of planet formation on stellar mass by finding planets around intermediate-mass giant stars. We present high accuracy RV measurements of the K1.5 III star 42 Dra and the K4 III star HD 139357. The wavelength reference for the RV measurements was provided by an iodine absorption cell placed in the optical path of the spectrograph.
- ID:
- ivo://CDS.VizieR/J/AJ/162/181
- Title:
- RVel & Hipparcos positions of epsilon Eridani
- Short Name:
- J/AJ/162/181
- Date:
- 14 Mar 2022 06:39:08
- Publisher:
- CDS
- Description:
- {epsilon}Eridani is a young planetary system hosting a complex multibelt debris disk and a confirmed Jupiter-like planet orbiting at 3.48au from its host star. Its age and architecture are thus reminiscent of the early Solar System. The most recent study of Mawet et al., which combined radial-velocity data and Ms-band direct imaging upper limits, started to constrain the planet's orbital parameters and mass, but are still affected by large error bars and degeneracies. Here we make use of the most recent data compilation from three different techniques to further refine {epsilon}Eridani b's properties: RVs, absolute astrometry measurements from the Hipparcos and Gaia missions, and new Keck/NIRC2 Ms-band vortex coronagraph images. We combine this data in a Bayesian framework. We find a new mass, M_b_=0.66_-0.09_^+0.12^M_Jup_, and inclination, i=78.81_-22.41_^+29.34^deg, with at least a factor 2 of improvement over previous uncertainties. We also report updated constraints on the longitude of the ascending node, the argument of the periastron, and the time of periastron passage. With these updated parameters, we can better predict the position of the planet at any past and future epoch, which can greatly help define the strategy and planning of future observations and with subsequent data analysis. In particular, these results can assist the search for a direct detection with JWST and the Nancy Grace Roman Space Telescope's coronagraph instrument.
- ID:
- ivo://CDS.VizieR/J/AJ/123/3154
- Title:
- RV light curves of variable stars in Leo A
- Short Name:
- J/AJ/123/3154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a search for short-period variable stars in Leo A. We have found 92 candidate variables, including eight candidate RR Lyrae stars. From the RR Lyrae stars, we measure a distance modulus of (m-M)0=24.51+/-0.12, or 0.80+/-0.04Mpc. This discovery of RR Lyrae stars confirms for the first time the presence of an ancient (older than ~11Gyr) population in Leo A, accounting for at least 0.1% of the galaxy's V luminosity. We have also discovered a halo of old (more than ~2Gyr) stars surrounding Leo A, with a scale length roughly 50% larger than that of the dominant young population. We also report the discovery of a large population of Cepheids in Leo A. The median absolute magnitude of our Cepheid sample is M_V_=-1.1, fainter than 96% of SMC and 99% of LMC Cepheids. Their periods are also unusual, with three Cepheids that are deduced to be pulsating in the fundamental mode having periods of under 1 day. Upon examination, these characteristics of the Leo A Cepheid population appear to be a natural extension of the classical Cepheid period-luminosity relations to low metallicity, rather than being indicative of a large population of "anomalous" Cepheids. We demonstrate that the periods and luminosities are consistent with the expected values of low-metallicity blue helium-burning stars (BHeB's), which populate the instability strip at lower luminosities than do higher metallicity BHeB's. Observations of Leo A were obtained at the WIYN 3.5 m telescope on the nights of 20-22 December 2000, using the MIMO camera.
- ID:
- ivo://CDS.VizieR/J/A+A/610/A17
- Title:
- RV of candidate hybrid variable stars
- Short Name:
- J/A+A/610/A17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Hundreds of candidate hybrid pulsators of intermediate type A-F were revealed by recent space missions. Hybrid pulsators allow us to study the full stellar interiors, where both low-order p- and high-order g-modes are simultaneously excited. The true hybrid stars must be identified since other processes, related to stellar multiplicity or rotation, might explain the presence of (some) low frequencies observed in their periodograms. We measured the radial velocities of 50 candidate delta Scuti - gamma Doradus hybrid stars from the Kepler mission with the Hermes and Ace spectrographs over a time span of months to years. We aim to derive the fraction of binary and multiple systems and to provide an independent and homogeneous determination of the atmospheric properties and v.sini for all targets. The long(er)-term objective is to identify the (probable) physical cause of the low frequencies. We computed one-dimensional cross-correlation functions (CCFs) in order to find the best set of parameters in terms of number of components, spectral type(s), and v.sini for each target. Fundamental parameters were determined by fitting (composite) synthetic spectra to the normalised median spectra corrected for the appropriate Doppler shifts. We report on the analysis of 478 high-resolution Hermes and 41 Ace spectra of A/F-type candidate hybrid pulsators from the Kepler field. We determined their radial velocities, projected rotational velocities, and atmospheric properties and classified our targets based on the shape of the CCFs and the temporal behaviour of the radial velocities. We derived orbital solutions for seven new systems. Three preliminary long-period orbital solutions are confirmed by a photometric time-delay analysis. Finally, we determined a global multiplicity fraction of 27 percent in our sample of candidate hybrid stars.
- ID:
- ivo://CDS.VizieR/J/AJ/160/151
- Title:
- RVs of 5 cataclysmic variable candidates
- Short Name:
- J/AJ/160/151
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report follow-up observations of five cataclysmic variable candidates from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) published by Hou et al. LAMOSTJ024048.51+195226.9 is the most unusual of the five; an early-M type secondary star contributes strongly to its spectrum, and its spectral and photometric behavior are strikingly reminiscent of the hitherto-unique propeller system AE Aqr. We confirm that a 7.34hr period discovered in the Catalina survey data is orbital. Another object, LAMOSTJ204305.95+341340.6, appears to be a near twin of the novalike variable V795Her, with an orbital period in the so-called 2-3hr "gap." LAMOSTJ035913.61+405035.0 is evidently an eclipsing, weakly outbursting dwarf nova with a 5.48hr period. Our spectrum of LAMOSTJ090150.09+375444.3 is dominated by a late-type secondary and shows weak, narrow Balmer emission moving in phase with the absorption lines, but at lower amplitude; we do not see the HeII {lambda}4686 emission evident in the published discovery spectrum. We again confirm that a period from the Catalina data, in this case 6.80hr, is orbital. LAMOSTJ033940.98+414805.7 yields a radial-velocity period of 3.54hr, and its spectrum appears to be typical of novalike variables in this period range. The spectroscopically selected sample from LAMOST evidently includes some interesting cataclysmic variables that have been unrecognized until now, apparently because of the relatively modest range of their photometric variations.
- ID:
- ivo://CDS.VizieR/J/A+A/657/A4
- Title:
- RVs of 18 Galactic luminous blue variable stars
- Short Name:
- J/A+A/657/A4
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Luminous blue variables (LBVs) are characterised by strong photometric and spectroscopic variability. They are thought to be in a transitory phase between O-type stars on the main sequence and the Wolf-Rayet stage. Recent studies also evoked the possibility that they might be formed through binary interaction. Only a few are known in binary systems so far, but their multiplicity fraction is still uncertain. We derive the binary fraction of the Galactic LBV population. We combine multi-epoch spectroscopy and long-baseline interferometry to probe separations from 0.1 to 120mas around confirmed and candidate LBVs. We used a cross-correlation technique to measure the radial velocities of these objects. We identified spectroscopic binaries through significant radial velocity variability with an amplitude larger than 35km/s. We also investigated the observational biases to take them into account when we established the intrinsic binary fraction. We used candid to detect interferometric companions, derive their flux fractions, and their positions on the sky. From the multi-epoch spectroscopy, we derive an observed spectroscopic binary fraction of 26-10+16%. Considering period and mass ratio ranges from log(Porb)=0-3 (i.e. from 1 to 1000days), q=0.1-1.0, and a representative set of orbital parameter distributions, we find a bias-corrected binary fraction of 62_-24_^+38^%. Based on data of the interferometric campaign, we detect a binary fraction of 70+/-9% at projected separations between 1 and 120mas. Based on the derived primary diameters and considering the distances of these objects, we measure for the first time the exact radii of Galactic LBVs to be between 100 and 650R_{sun}_. This means that it is unlikely that short-period systems are included among LBV-like stars. This analysis shows for the first time that the binary fraction in the Galactic LBV population is large. If they form through single-star evolution, their orbit must be large initially. If they form through a binary channel, the implication is that either massive stars in short binary systems must undergo a phase of fully non-conservative mass transfer to be able to sufficiently widen the orbit to form an LBV, or that LBVs form through merging in initially binary or triple systems. Interferometric follow-up would provide the distributions of orbital parameters at more advanced stages and would serve to quantitatively test the binary evolution in massive stars.
- ID:
- ivo://CDS.VizieR/J/A+A/633/A37
- Title:
- RXJ1604.3-2130A griz and JHK light curves
- Short Name:
- J/A+A/633/A37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- RX J1604.3-2130A is a young, dipper-type, variable star in the Upper Scorpius association, suspected to have an inclined inner disk with respect to its face-on outer disk. We study the eclipses to constrain the inner disk properties. We use time-resolved photometry from the Rapid Eye Mount telescope and Kepler 2 data to study the multi-wavelength variability, and archival optical and IR data to track accretion, rotation, and changes in disk structure. The observations reveal details of the structure and matter transport through the inner disk. The eclipses show 5d quasi-periodicity, with the phase drifting in time and some periods showing increased/decreased eclipse depth and frequency. Dips are consistent with extinction by slightly processed dust grains in an inclined, irregularly-shaped inner disk locked to the star through two relatively stable accretion structures. The grains are located near the dust sublimation radius (~0.09au) at the corotation radius, and can explain the shadows observed in the outer disk. The total mass (gas and dust) required to produce the eclipses and shadows is a few % of a Ceres mass. Such amount of mass is accreted/replenished by accretion in days to weeks, which explains the variability from period to period. Spitzer and WISE variability reveal variations in the dust content in the innermost disk on a few years timescale, which is consistent with small imbalances (compared to the stellar accretion rate) in the matter transport from the outer to the inner disk. A decrease in the accretion rate is observed at the times of less eclipsing variability and low mid-IR fluxes, confirming this picture. The vsini=16km/s confirms that the star cannot be aligned with the outer disk, but is likely close to equator-on and to be aligned with the inner disk. This anomalous orientation is a challenge for standard theories of protoplanetary disk formation.
- ID:
- ivo://CDS.VizieR/J/PAZh/37/924
- Title:
- 1RXS J073346.0+261933 light curve
- Short Name:
- J/PAZh/37/924
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the course of our search for the optical identifications of ROSAT X-ray sources, we have found a highly variable object with a very unusual behavior on long time scales, rare color indices, and a high X-ray-to-optical flux ratio. We present the archival light curve from the Catalina Sky Survey, optical spectroscopy from RTT150, and time-resolved photometry from the Astrotel-Caucasus telescope. The object appears to be a magnetic cataclysmic variable (a polar) with an orbital period P=3.20h.
