- ID:
- ivo://CDS.VizieR/J/ApJ/832/121
- Title:
- 4-yr RV survey of red giant in eclipsing binaries
- Short Name:
- J/ApJ/832/121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Given the potential of ensemble asteroseismology for understanding fundamental properties of large numbers of stars, it is critical to determine the accuracy of the scaling relations on which these measurements are based. From several powerful validation techniques, all indications so far show that stellar radius estimates from the asteroseismic scaling relations are accurate to within a few percent. Eclipsing binary systems hosting at least one star with detectable solar-like oscillations constitute the ideal test objects for validating asteroseismic radius and mass inferences. By combining radial velocity (RV) measurements and photometric time series of eclipses, it is possible to determine the masses and radii of each component of a double-lined spectroscopic binary. We report the results of a four-year RV survey performed with the echelle spectrometer of the Astrophysical Research Consortium's 3.5m telescope and the APOGEE spectrometer at Apache Point Observatory. We compare the masses and radii of 10 red giants (RGs) obtained by combining radial velocities and eclipse photometry with the estimates from the asteroseismic scaling relations. We find that the asteroseismic scaling relations overestimate RG radii by about 5% on average and masses by about 15% for stars at various stages of RG evolution. Systematic overestimation of mass leads to underestimation of stellar age, which can have important implications for ensemble asteroseismology used for Galactic studies. As part of a second objective, where asteroseismology is used for understanding binary systems, we confirm that oscillations of RGs in close binaries can be suppressed enough to be undetectable, a hypothesis that was proposed in a previous work.
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- ID:
- ivo://CDS.VizieR/J/ApJ/837/30
- Title:
- 25yrs monitoring of stellar orbits in the GC
- Short Name:
- J/ApJ/837/30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using 25 years of data from uninterrupted monitoring of stellar orbits in the Galactic Center (GC), we present an update of the main results from this unique data set: a measurement of mass and distance to SgrA*. Our progress is not only due to the eight-year increase in time base, but also to the improved definition of the coordinate system. The star S2 continues to yield the best constraints on the mass of and distance to Sgr A*; the statistical errors of 0.13x10^6^M_{sun}_ and 0.12kpc have halved compared to the previous study. The S2 orbit fit is robust and does not need any prior information. Using coordinate system priors, the star S1 also yields tight constraints on mass and distance. For a combined orbit fit, we use 17 stars, which yields our current best estimates for mass and distance: M=4.28+/-0.10|_stat._+/-0.21|_sys_x10^6^M_{sun}_ and R_0_=8.32+/-0.07|_stat._+/-0.14|_sys_kpc. These numbers are in agreement with the recent determination of R_0_ from the statistical cluster parallax. The positions of the mass, of the near-infrared flares from Sgr A*, and of the radio source Sgr A* agree to within 1mas. In total, we have determined orbits for 40 stars so far, a sample which consists of 32 stars with randomly oriented orbits and a thermal eccentricity distribution, plus eight stars that we can explicitly show are members of the clockwise disk of young stars, and which have lower-eccentricity orbits.
- ID:
- ivo://CDS.VizieR/J/ApJ/836/124
- Title:
- 2yrs of eclipse data & precise RVs for LP661-13
- Short Name:
- J/ApJ/836/124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the detection of stellar eclipses in the LP 661-13 system. We present the discovery and characterization of this system, including high-resolution spectroscopic radial velocities and a photometric solution spanning two observing seasons. LP 661-13 is a low-mass binary system with an orbital period of 4.7043512_-0.0000010_^+0.0000013^d at a distance of 24.9+/-1.3pc. LP661-13A is a 0.30795+/-0.00084M_{sun}_ star, while LP661-13B is a 0.19400+/-0.00034M_{sun}_ star. The radius of each component is 0.3226+/-0.0033R_{sun}_ and 0.2174+/-0.0023R_{sun}_, respectively. We detect out-of-eclipse modulations at a period slightly shorter than the orbital period, implying that at least one of the components is not rotating synchronously. We find that each component is slightly inflated compared to stellar models, and that this cannot be reconciled through age or metallicity effects. As a nearby eclipsing binary system, where both components are near or below the full-convection limit, LP 661-13 will be a valuable test of models for the structure of cool dwarf stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/854/12
- Title:
- 16yrs of radial velocity measurements of S0-2
- Short Name:
- J/ApJ/854/12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The star S0-2, which orbits the supermassive black hole (SMBH) in our Galaxy with a period of 16 years, provides the strongest constraint on both the mass of the SMBH and the distance to the Galactic center. S0-2 will soon provide the first measurement of relativistic effects near a SMBH. We report the first limits on the binarity of S0-2 from radial velocity (RV) monitoring, which has implications for both understanding its origin and robustness as a probe of the central gravitational field. With 87 RV measurements, which include 12 new observations that we present, we have the requisite data set to look for RV variations from S0-2's orbital model. Using a Lomb-Scargle analysis and orbit- fitting for potential binaries, we detect no RV variation beyond S0-2's orbital motion and do not find any significant periodic signal. The lack of a binary companion does not currently distinguish different formation scenarios for S0-2. The upper limit on the mass of a companion star (M_comp_) still allowed by our results has a median upper limit of M_comp_ sin i <=1.6M_{sun}_ for periods between 1 and 150 days, the longest period to avoid tidal break-up of the binary. We also investigate the impact of the remaining allowed binary system on the measurement of the relativistic redshift at S0-2's closest approach in 2018. While binary star systems are important to consider for this experiment, we find that plausible binaries for S0-2 will not alter a 5{sigma} detection of the relativistic redshift.
- ID:
- ivo://CDS.VizieR/J/ApJ/821/89
- Title:
- 12yrs of radial velocity obs. of exoplanet systems
- Short Name:
- J/ApJ/821/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We conducted a Doppler survey at Keck combined with NIRC2 K-band adaptive optics (AO) imaging to search for massive, long-period companions to 123 known exoplanet systems with one or two planets detected using the radial velocity (RV) method. Our survey is sensitive to Jupiter-mass planets out to 20au for a majority of stars in our sample, and we report the discovery of eight new long-period planets, in addition to 20 systems with statistically significant RV trends that indicate the presence of an outer companion beyond 5AU. We combine our RV observations with AO imaging to determine the range of allowed masses and orbital separations for these companions, and account for variations in our sensitivity to companions among stars in our sample. We estimate the total occurrence rate of companions in our sample to be 52+/-5% over the range 1-20M_Jup_ and 5-20AU. Our data also suggest a declining frequency for gas giant planets in these systems beyond 3-10AU, in contrast to earlier studies that found a rising frequency for giant planets in the range 0.01-3AU. This suggests either that the frequency of gas giant planets peaks between 3 and 10 AU, or that outer companions in these systems have a different semi-major axis distribution than the overall population of gas giant planets. Our results also suggest that hot gas giants may be more likely to have an outer companion than cold gas giants. We find that planets with an outer companion have higher average eccentricities than their single counterparts, suggesting that dynamical interactions between planets may play an important role in these systems.
- ID:
- ivo://CDS.VizieR/J/AJ/144/173
- Title:
- YSOs from SED fitting in six HII regions
- Short Name:
- J/AJ/144/173
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigated six HII regions with infrared, bright rimmed bubble or cometary morphology, in search of quantitative evidence for triggered star formation, both collect and collapse and radiatively driven implosion (RDI). We identified and classified 458 young stellar objects (YSOs) in and around the HII regions. YSOs were determined by fitting a collection of radiative transfer model spectral energy distributions to infrared photometry for a large sample of point sources. We determined areas where there exist enhanced populations of relatively unevolved YSOs on the bright rims of these regions, suggesting that star formation has been triggered there. We further investigated the physical properties of the regions by using radio continuum emission as a proxy for ionizing flux powering the HII regions, and ^13^CO(1-0) observations to measure masses and gravitational stability of molecular clumps. We used an analytical model of collect and collapse triggered star formation, as well as a simulation of RDI, and thus we compare the observed properties of the molecular gas with those predicted in the triggering scenarios. Notably, those regions in our sample that show evidence of cometary, or "blister", morphology are more likely to show evidence of triggering.
- ID:
- ivo://CDS.VizieR/J/A+A/636/A119
- Title:
- YZ Ceti CARMENES and HARPS radial velocity curve
- Short Name:
- J/A+A/636/A119
- Date:
- 25 Oct 2021 00:44:17
- Publisher:
- CDS
- Description:
- The nearby ultra-compact multiplanetary system YZ Ceti consists of at least three planets, and a fourth tentative signal. The orbital period of each planet is the subject of discussion in the literature due to strong aliasing in the radial velocity data. The stellar activity of this M dwarf also hampers significantly the derivation of the planetary parameters. With an additional 229 radial velocity measurements obtained since the discovery publication, we reanalyze the YZ Ceti system and resolve the alias issues. We use model comparison in the framework of Bayesian statistics and periodogram simulations based on a method by Dawson and Fabrycky to resolve the aliases. We discuss additional signals in the RV data, and derive the planetary parameters by simultaneously modeling the stellar activity with a Gaussian process regression model. To constrain the planetary parameters further we apply a stability analysis on our ensemble of Keplerian fits. We find no evidence for a fourth possible companion. We resolve the aliases: the three planets orbit the star with periods of 2.02d, 3.06d, and 4.66d. We also investigate an effect of the stellar rotational signal on the derivation of the planetary parameters, in particular the eccentricity of the innermost planet. Using photometry we determine the stellar rotational period to be close to 68d and we also detect this signal in the residuals of a three-planet fit to the RV data and the spectral activity indicators. From our stability analysis we derive a lower limit on the inclination of the system with the assumption of coplanar orbits which is i_min_=0.9deg. From the absence of a transit event with TESS, we derive an upper limit of the inclination of i_max_=87.43deg. YZ Ceti is a prime example of a system where strong aliasing hindered the determination of the orbital periods of exoplanets. Additionally, stellar activity influences the derivation of planetary parameters and modeling them correctly is important for the reliable estimation of the orbital parameters in this specific compact system. Stability considerations then allow additional constraints to be placed on the planetary parameters.
- ID:
- ivo://CDS.VizieR/J/A+A/605/L11
- Title:
- YZ Ceti radial velocity curve
- Short Name:
- J/A+A/605/L11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Exoplanet surveys have shown that systems with multiple low-mass planets on compact orbits are common. Except for a few cases, however, the masses of these planets are generally unknown. At the very end of the main sequence, host stars have the lowest mass and hence offer the largest reflect motion for a given planet. In this context, we monitored the low-mass (0.13M_{sun}_) M dwarf YZ Cet (GJ 54.1, HIP 5643) intensively and obtained radial velocities and stellar-activity indicators derived from spectroscopy and photometry, respectively. We find strong evidence that it is orbited by at least three planets in compact orbits (Porb=1.97, 3.06, 4.66 days), with the inner two near a 2:3 mean-motion resonance. The minimum masses are comparable to the mass of Earth (Msini=0.75+/-0.13, 0.98+/-0.14, and 1.14+/-0.17M_{earth}_), and they are also the lowest masses measured by radial velocity so far. We note the possibility for a fourth planet with an even lower mass of Msini=0.472+/-0.096 Mearth at Porb=1.04-days. An n-body dynamical model is used to place further constraints on the system parameters. At 3.6 parsecs, YZ Cet is the nearest multi-planet system detected to date.