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- ID:
- ivo://CDS.VizieR/J/ApJ/804/30
- Title:
- Robo-AO observed cool subdwarf companions
- Short Name:
- J/ApJ/804/30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Cool subdwarfs are the oldest members of the low-mass stellar population. Mostly present in the galactic halo, subdwarfs are characterized by their low-metallicity. Measuring their binary fraction and comparing it to solar-metallicity stars could give key insights into the star formation process early in the Milky Way's history. However, because of their low luminosity and relative rarity in the solar neighborhood, binarity surveys of cool subdwarfs have suffered from small sample sizes and incompleteness. Previous surveys have suggested that the binary fraction of red subdwarfs is much lower than for their main-sequence cousins. Using the highly efficient Robo-AO system, we present the largest high-resolution survey of subdwarfs, sensitive to angular separations ({rho}>=0.15") and contrast ratios ({Delta}_mi_<=6) invisible in past surveys. Of 344 target cool subdwarfs, 43 are in multiple systems, 19 of which are newly discovered, for a binary fraction of 12.5+/-1.9%. We also discovered seven triple star systems for a triplet fraction of 2.0+/-0.8%. Comparisons to similar surveys of solar-metallicity dwarf stars gives a ~3{sigma} disparity in luminosity between companion stars, with subdwarfs displaying a shortage of low-contrast companions. We also observe a lack of close subdwarf companions in comparison to similar-mass dwarf multiple systems.
- ID:
- ivo://CDS.VizieR/J/ApJ/704/750
- Title:
- Rotational behavior of metal-poor stars
- Short Name:
- J/ApJ/704/750
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper describes the behavior of the rotational velocity in metal-poor stars ([Fe/H]<=-0.5dex) in different evolutionary stages, based on vsini values from the literature. Our sample is comprised of stars in the field and some Galactic globular clusters, including stars on the main sequence, the red giant branch (RGB), and the horizontal branch (HB). The metal-poor stars are, mainly, slow rotators, and their vsini distribution along the HR diagram is quite homogeneous. Nevertheless, a few moderate to high values of vsini are found in stars located on the main sequence and the HB. We show that the overall distribution of vsini values is basically independent of metallicity for the stars in our sample. We present an extensive tabulation of all quantities discussed in this paper, including rotation velocities, temperatures, gravities, and metallicities [Fe/H], as well as broadband magnitudes and colors.
- ID:
- ivo://CDS.VizieR/J/ApJ/702/489
- Title:
- ROTSE observations of gamma-ray burst afterglows
- Short Name:
- J/ApJ/702/489
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on a complete set of early optical afterglows of gamma-ray bursts (GRBs) obtained with the Robotic Optical Transient Search Experiment (ROTSE-III) telescope network from 2005 March through 2007 June. This set is comprised of 12 afterglows with early optical and Swift/X-Ray Telescope observations, with a median ROTSE-III response time of 45s after the start of {gamma}-ray emission (8s after the GCN notice time). These afterglows span 4 orders of magnitude in optical luminosity, and the contemporaneous X-ray detections allow multi-wavelength spectral analysis. Excluding X-ray flares, the broadband synchrotron spectra show that the optical and X-ray emission originate in a common region, consistent with predictions of the external forward shock in the fireball model. However, the fireball model is inadequate to predict the temporal decay indices of the early afterglows, even after accounting for possible long-duration continuous energy injection. We find that the optical afterglow is a clean tracer of the forward shock, and we use the peak time of the forward shock to estimate the initial bulk Lorentz factor of the GRB outflow, and find 100<~{Gamma}_0_<~1000, consistent with expectations.
345. RR Lyrae in NGC 6171
- ID:
- ivo://CDS.VizieR/J/AJ/113/1711
- Title:
- RR Lyrae in NGC 6171
- Short Name:
- J/AJ/113/1711
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- CCD observations have been used to derive precise light curves and Fourier parameters for sixteen RR Lyrae variables in the Oosterhoff type I globular cluster NGC 6171. It is found that, for the RRab stars, the Fourier phase differences {phi}_21_, {phi}_31_ and {phi}_41_ all correlate with period, but the amplitude ratios R_21_, R_31_, and R_41_ do not. For the RRc stars, R_21_, {phi}_31_, and {phi}_41_ correlate with period, but {phi}_21_, R_31_, and R_41_ do not. It is also found that a plot of R_21_ against {phi}_21_ is a useful tool for distinguishing between RRc and RRab stars, regardless of color or chemical composition. Simon's method that relates physical properties of RRc stars to the pulsation period and Fourier phase parameter {phi}_31_ has been used to determine the mass, luminosity, temperature and a helium parameter for the RRc stars. A comparison with the parameters determined from CCD observations of RRc stars in six other galactic globular clusters indicates that mean masses and mean luminosities increase and mean temperatures and helium abundances decrease with decreasing cluster metal abundance. The formulae of Jurcsik & Kovacs (1996, Cat. <J/A+A/312/111>) for relating Fourier parameters of RRab stars to [Fe/H] and luminosity have been tested and the results are reasonable. (c) 1997 American Astronomical Society.
- ID:
- ivo://CDS.VizieR/J/A+A/375/909
- Title:
- RR Lyrae stars in the Sgr dwarf
- Short Name:
- J/A+A/375/909
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We carried out a period analysis on ~3700 RR Lyrae stars on two Schmidt fields centred on (l, b)=(3.1{deg}, -77.1{deg}) and (6.6{deg}, -10.8{deg}) respectively, covering an area of ~50{deg}^2^. These stars are distributed almost evenly between the Sagittarius dwarf galaxy (Sgr) and the Milky Way. Files in the "lcurves" directory are the light curves of the multi-periodic RR Lyraes discovered towards the Sgr dwarf galaxy. This set includes stars in Sgr and also foreground Galactic RR Lyraes.
- ID:
- ivo://CDS.VizieR/J/A+A/357/871
- Title:
- RR Lyrae stars in the Sgr dwarf galaxy
- Short Name:
- J/A+A/357/871
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We carried out a search for RR Lyrae stars towards the Sagittarius dwarf galaxy based on two series of photographic Schmidt plates. This search yielded 4013 RR Lyrae stars (3947 mono-periodic, and 66 multi-periodic) spread over ~50 square degrees between Galactic latitudes b=-4{deg} and b=-15{deg}. The analysis of this catalog of RR Lyraes allowed us to map the structure of the Sagittarius dwarf galaxy behind the high density of Galactic foreground stars (this paper, Paper I), and to study the properties of the old stellar population in the Sgr dwarf (Paper II, Cseresnjes, 2001, Cat. <J/A+A/375/909>).
- ID:
- ivo://CDS.VizieR/J/A+A/639/A35
- Title:
- RV jitter and photometric var. correlation
- Short Name:
- J/A+A/639/A35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Characterizing the relation between stellar photometric variability and radial velocity (RV) jitter can help us to better understand the physics behind these phenomena. The current and upcoming high precision photometric surveys such as TESS, CHEOPS, and PLATO will provide the community with thousands of new exoplanet candidates. As a consequence, the presence of such a correlation is crucial in selecting the targets with the lowest RV jitter for efficient RV follow-up of exoplanetary candidates. Studies of this type are also crucial to design optimized observational strategies to mitigate RV jitter when searching for Earth-mass exoplanets. Aims. Our goal is to assess the correlation between high-precision photometric variability measurements and high-precision RV jitter over different time scales. We analyze 171 G, K, and M stars with available TESS high precision photometric time-series and HARPS precise RVs. We derived the stellar parameters for the stars in our sample and measured the RV jitter and photometric variability. We also estimated chromospheric CaII H & K activity indicator log(R'_HK_), vsini, and the stellar rotational period. Finally, we evaluate how different stellar parameters and an RV sampling subset can have an impact on the potential correlations. We find a varying correlation between the photometric variability and RV jitter as function of time intervals between the TESS photometric observation and HARPS RV. As the time intervals of the observations considered for the analysis increases, the correlation value and significance becomes smaller and weaker, to the point that it becomes negligible. We also find that for stars with a photometric variability above 6.5 ppt the correlation is significantly stronger. We show that such a result can be due to the transition between the spot-dominated and the faculae-dominated regime. We quantified the correlations and updated the relationship between chromospheric CaII H & K activity indicator log(R'_HK_) and RV jitter.
- ID:
- ivo://CDS.VizieR/J/ApJS/247/11
- Title:
- RV photon limits of well-characterized F-M stars
- Short Name:
- J/ApJS/247/11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The determination of extrasolar planet masses with the radial velocity (RV) technique requires spectroscopic Doppler information from the planet's host star, which varies with stellar brightness and temperature. We analyze the Doppler information in spectra from dwarfs of spectral types F-M utilizing empirical information from HARPS and CARMENES data and model spectra. We revisit the question of whether optical or near-infrared instruments are more efficient for RV observations in low-mass stars, and we come to the conclusion that an optical setup (BVR bands) is more efficient than a near-infrared one (YJHK) in dwarf stars hotter than 3200K. We publish a catalog of 46480 well-studied F-M dwarfs in the solar neighborhood, and we compare its distribution to more than 1 million stars from Gaia DR2. For all stars, we estimate the RV photon noise achievable in typical observations under the assumption of no activity jitter and slow rotation. We find that with an ESPRESSO-like instrument at an 8m telescope, a photon noise limit of 10cm/s or lower can be reached in more than 280 stars in a 5 minute observation. At 4m telescopes, a photon noise limit of 1m/s can be reached in a 10 minute exposure in approximately 10000 predominantly Sun-like stars with a HARPS-like (optical) instrument. The same applies to ~3000 stars for a red optical setup that covers the R and I bands and ~700 stars for a near-infrared instrument. For the latter two, many of the targets are nearby M dwarfs. Finally, we identify targets in which Earth-mass planets within the liquid water habitable zone can cause RV amplitudes comparable to the RV photon noise. Assuming the same exposure times as above, we find that an ESPRESSO-like instrument can reach this limit for 1M_{Earth}_ planets in more than 1000 stars. The optical, red optical, and near-infrared configurations reach the limit for 2M_{Earth}_ planets in approximately 500, 700, and 200 stars, respectively. An online tool is provided to estimate the RV photon noise as a function of stellar temperature and brightness and wavelength coverage.
- ID:
- ivo://CDS.VizieR/I/222
- Title:
- San Fernando AC Zone Data Reduced to ACRS
- Short Name:
- I/222
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The U.S. Naval Observatory is in the process of making new reductions of the Astrographic Catalogue (AC) using a modern reference system, the ACRS, which represents the system of the FK5. The data from the San Fernando Zone, whose plates are centered between declinations -3 and -9 degrees (eq. 1900), have been analyzed for scale, rotation, tilt, coma, magnitude equation, radial distortion and distortions introduced by the use of reseaux in the Carte du Ciel program. The result is a positional catalog of over 225,000 stars on eq. J2000.0, epoch of observation. Additionally, all stars have been matched with the Tycho Input Catalog (revised); those numbers have been added for additional identification purposes.
