- ID:
- ivo://CDS.VizieR/J/A+A/610/A3
- Title:
- Radial velocity curve of 3 K giants
- Short Name:
- J/A+A/610/A3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The purpose of this paper is to detect and investigate the nature of long-term radial velocity (RV) variations of K-type giants and to confirm planetary companions around the stars. We have conducted two planet search programs by precise RV measurement using the 1.8m telescope at Bohyunsan Optical Astronomy Observatory (BOAO) and the 1.88m telescope at Okayama Astrophysical Observatory (OAO). The BOAO program searches for planets around 55 early K giants. The OAO program is looking for 190 G-K type giants. In this paper, we report the detection of long-period RV variations of three K giant stars, HD 40956, HD 111591, and HD 113996. We investigated the cause of the observed RV variations and conclude the substellar companions are most likely the cause of the RV variations. The orbital analyses yield P=578.6+/-3.3d, msini=2.7+/-0.6M_J_, a=1.4+/-0.1AU for HD 40956; P=1056.4+/-14.3d, msini=4.4+/-0.4M_J_, a=2.5+/-0.1AU for HD 111591; P=610.2+/-3.8d, msini=6.3+/-1.0M_J_, a=1.6+/-0.1AU for HD 113996.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/566/A113
- Title:
- Radial velocity curves of HIP105854
- Short Name:
- J/A+A/566/A113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We are conducting a radial velocity survey called EXPRESS (EXoPlanets aRound Evolved StarS) of a sample of 166 giant stars aimed at studying the population of close-in planets and how their orbital properties are influenced by the host star evolution. We present precision radial velocity measurements of the giant star HIP 105854, which have revealed the presence of a massive giant planet in a 184-days orbit.
- ID:
- ivo://CDS.VizieR/J/AJ/148/118
- Title:
- Radial velocity curves of LMC ellipsoidal variables
- Short Name:
- J/AJ/148/118
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Ellipsoidal red giant binaries are close binary systems where an unseen, relatively close companion distorts the red giant, leading to light variations as the red giant moves around its orbit. These binaries are likely to be the immediate evolutionary precursors of close binary planetary nebula and post-asymptotic giant branch and post-red giant branch stars. Due to the MACHO and OGLE photometric monitoring projects, the light variability nature of these ellipsoidal variables has been well studied. However, due to the lack of radial velocity curves, the nature of their masses, separations, and other orbital details has so far remained largely unknown. In order to improve this situation, we have carried out spectral monitoring observations of a large sample of 80 ellipsoidal variables in the Large Magellanic Cloud and we have derived radial velocity curves. At least 12 radial velocity points with good quality were obtained for most of the ellipsoidal variables. The radial velocity data are provided with this paper. Combining the photometric and radial velocity data, we present some statistical results related to the binary properties of these ellipsoidal variables.
- ID:
- ivo://CDS.VizieR/J/A+A/647/A160
- Title:
- Radial velocity data of epsilon Cyg
- Short Name:
- J/A+A/647/A160
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the Hamilton Echelle Spectrograph at Lick Observatory, we have obtained precise radial velocities of a sample of 373 G- and K-giant stars from 1999 until 2012, leading to the discovery of several single and multiple planetary systems. The radial velocities of the long-period (~53 years) spectroscopic binary epsilon Cyg (HIP 102488) are found to exhibit additional variations with a much shorter period (~291 days). This signature is not perfectly regular, as its period and amplitude seem to change over time. We intend to improve the orbital solution of the epsilon Cyg system, and attempt to identify the cause of the nearly periodic shorter period variations, which might be due to an additional substellar companion. We use precise radial velocity measurements of the K-giant star epsilon Cyg from Lick Observatory, in combination with a large set of RVs collected more recently with the SONG telescope, as well as archival data sets.
- ID:
- ivo://CDS.VizieR/J/A+A/595/A55
- Title:
- Radial velocity data of HD 59686 A
- Short Name:
- J/A+A/595/A55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- For over 12 years, we have carried out a precise radial velocity (RV) survey of a sample of 373 G- and K-giant stars using the Hamilton Echelle Spectrograph at the Lick Observatory. There are, among others, a number of multiple planetary systems in our sample as well as several planetary candidates in stellar binaries. We aim at detecting and characterizing substellar and stellar companions to the giant star HD 59686 A (HR 2877, HIP 36616). We obtained high-precision RV measurements of the star HD 59686 A. By fitting a Keplerian model to the periodic changes in the RVs, we can assess the nature of companions in the system. To distinguish between RV variations that are due to non-radial pulsation or stellar spots, we used infrared RVs taken with the CRIRES spectrograph at the Very Large Telescope. Additionally, to characterize the system in more detail, we obtained high-resolution images with LMIRCam at the Large Binocular Telescope.
- ID:
- ivo://CDS.VizieR/J/A+A/628/A106
- Title:
- Radial velocity time series of EK Eridani
- Short Name:
- J/A+A/628/A106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present further evidence of acoustic oscillations in the slowly rotating overactive G8 sub-giant EK Eri. This star was observed with the 1m Hertzsprung SONG telescope at the Observatorio del Teide for two different runs of 8 and 13 nights, respectively, that were separated by about a year. We determined a significant excess of power around {nu}_max_=253+/-3uHz in the first observing run and were able to determine a large separation, {Delta}_{nu}_=16.430+/-22uHz. No significant excess of power was instead detected in a subsequent SONG observing season, as also supported by our analysis of the simultaneous TESS photometric observations. We propose a new amplitude-luminosity relation in order to account for the missing power in the power spectrum. Based on the evolutionary stage of this object, we argue that a standard {alpha}^2^{OMEGA} dynamo cannot be excluded as the possible origin for the observed magnetic field.
- ID:
- ivo://CDS.VizieR/J/A+A/625/A33
- Title:
- Radial velocity time series of HD 122563
- Short Name:
- J/A+A/625/A33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The nearby metal-poor giant HD122563 is an important astrophysical laboratory in which to test stellar atmospheric and interior physics. It is also a benchmark star for which to calibrate methods to apply to large scale surveys. Recently it has been remeasured using various methodologies given the new high precision instruments at our disposal. However, inconsistencies in the observations and models have been found. In order to better characterise this star using complementary techniques we have been measuring its radial velocities since 2016 using the Hertzsprung telescope (SONG network node) in order to detect oscillations. In this work we report the first detections of sun-like oscillations in this star, and to our knowledge, a detection in the most metal-poor giant to date. We applied the classical seismic scaling relation to derive a new surface gravity for HD122563 of logg=1.39+/-0.01dex. Reasonable constraints on the mass imposed by its PopII giant classification then yields a radius of 30.8+/-1.0R_{sun}_. By coupling this new radius with recent interferometric measurements we infer a distance to the star of 306+/-9pc. This result places it further away than was previously thought and is inconsistent with the Hipparcos parallax. Independent data from the Gaia mission corroborate the distance hypothesis (d_GDR2_=290+/-5pc), and thus the updated fundamental parameters. We confirm the validity of the classical seismic scaling relation for surface gravity in metal-poor and evolved star regimes. The remaining discrepancy of 0.04dex between logg_GDR2_ (=1.43+/-0.03) reduces to 0.02dex by applying corrections to the scaling relations based on the mean molecular weight and adiabatic exponent. The new constraints on the HR diagram (L_*v_=381+/-26L_{sun}_) significantly reduce the disagreement between the stellar parameters and evolution models, however, a discrepancy of the order of 150K still exists. Fine-tuned stellar evolution calculations show that this discrepancy can be reconciled by changing the mixing-length parameter by an amount (-0.35) that is in agreement with predictions from recent 3D simulations and empirical results. Asteroseismic measurements are continuing, and analysis of the full frequency data complemented by a distance estimate promises to bring important constraints on our understanding of this star and of the accurate calibration of the seismic scaling relations in this regime.
- ID:
- ivo://CDS.VizieR/J/A+A/281/161
- Title:
- Radio emission from stars at 250GHz
- Short Name:
- J/A+A/281/161
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used the IRAM 30 m-telescope together with the Max Planck Institute for Radio Astronomy (MPIfR) bolometer to survey nearly 270 stars of different types for 250GHz continuum emission. We compare these data with their low frequency (cm-range) properties. Early type stars show very often a deviation from the uniformly expanding wind model which we tentatively attribute to temperature and/or density fluctuations in their deeper atmospheric layers. For WR stars this deviation seems to depend on the effective temperature. Pre-main sequence stars usually seem to be surrounded by a shell of warm dust making a substantial contribution to the 250 GHz flux density value. We have found especially for nearby giants and supergiants that a layer at the transition from photosphere to chromosphere emits ample 250 GHz radiation. We show that the present data can still be explained by a simple uniformly illuminated disk model with the known stellar radius. Optically variable stars are not very strong emitters at 250 GHz. We preferentially detected the more exotic ones, a few Beta Lyr-type and symbiotic stars. Comments on many individual objects are given in the appropriate sections.
- ID:
- ivo://CDS.VizieR/J/ApJ/737/9
- Title:
- RAVE spectroscopic data of stars in the thick disk
- Short Name:
- J/ApJ/737/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have undertaken the study of the elemental abundances and kinematic properties of a metal-poor sample of candidate thick-disk stars selected from the Radial Velocity Experiment spectroscopic survey of bright stars to differentiate among the present scenarios of the formation of the thick disk. In this paper, we report on a sample of 214 red giant branch, 31 red clump/horizontal branch, and 74 main-sequence/sub-giant branch metal-poor stars, which serves to augment our previous sample of only giant stars. We find that the thick disk [{alpha}/Fe] ratios are enhanced and have little variation (<0.1dex), in agreement with our previous study. The augmented sample further allows, for the first time, investigation of the gradients in the metal-poor thick disk.
- ID:
- ivo://CDS.VizieR/J/A+A/644/A45
- Title:
- R Crt and RT Vir Medicina spectra
- Short Name:
- J/A+A/644/A45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Water masers emitting at a radiofrequency of 22GHz are often found in the circumstellar envelopes of evolved stars. We monitored the H_2_O maser emission of a larger sample of evolved stars of different types to study the maser properties as a function of stellar type. We wish to understand the origin and evolution of the H_2_O masers in circumstellar envelopes. In this paper, we take a closer look at R Crt and RT Vir, two nearby (<250pc) semi-regular variable stars. The findings complement our monitoring results for RX Boo and SV Peg, two other semi-regular variable stars that we have discussed in a previous paper. Within the framework of the Medicina/Effelsberg H_2_O maser monitoring programme, we observed the maser emission of R Crt and RT Vir for more than two decades with single-dish telescopes. To get insights into the distribution of maser spots in the circumstellar envelopes at different times, to get an idea of their longevity, and, where possible, to be able to link the phenomena seen in our observations to maser locations within the envelopes, we collected interferometric data for these stars, taken within the same period, from the literature. The H_2_O masers in R Crt and RT Vir exhibit brightness variations on a variety of timescales. We confirm short-time variations of individual features on timescales of months to up to 1.5 years, as seen by previous monitoring programmes. Also decade-long variations of the general brightness level, independent from individual features, were seen in both stars. These long-term variations are attributed to brightness variations occurring independently from each other in selected velocity ranges and they are independent of the optical light curve of the stars. Expected drifts in velocity of individual features are usually masked by the blending of other features with similar velocities. However, in RT Vir, we found the exceptional case of a single feature with a constant velocity over 7.5 years (<0.06km/s/yr). We attribute the long-term brightness variations to the presence of regions with higher-than-average density in the stellar wind and hosting several clouds which emit maser radiation on short timescales. These regions typically need ~20 years to cross the H_2_O maser shell, where the right conditions for exciting H_2_O masers are present. Different clouds contained in such a region all move within a narrow range of velocities, and so does their maser emission. This sometimes gives the impression of longer-living features in single-dish spectra, in spite of the short lifetimes of the individual components that lie at their origin, thus, naturally explaining the longer timescales observed. The constant velocity feature (11km/s) is likely to come from a single maser cloud, which moved through about half of RT Vir's H_2_O maser shell without changing its velocity. From this, we infer that its path was located in the outer part of the H_2_O maser shell, where RT Vir's stellar wind has, apparently, already reached its terminal outflow velocity. This conclusion is independently corroborated by the observation that the highest H_2_O maser outflow velocity in RT Vir approaches the terminal outflow velocity, as given by OH and CO observations. This is generally not observed in other semi-regular variable stars. All four stars in our study are of optical variability type SRb, indicating the absence of periodic large-amplitude variations. Therefore, any likely responses of the maser brightness to variations of the optical emission are masked by the strong short-term maser fluctuations.
