Refining the Stellar Parameters of τ Ceti: a Pole-on Solar Analog

Context. Stellar evolution models are highly dependent on accurate mass estimates, especially for highly massive stars in the early stages of stellar evolution. The most direct method for obtaining model-independent stellar masses is derivation from the orbit of close binaries. Aims. Our aim was to derive the first astrometric plus radial velocity orbit solution for the single-lined spectroscopic binary star MWC 166 A, based on near-infrared interferometry over multiple epochs and ∼100 archival radial velocity measurements, and to derive fundamental stellar parameters from this orbit. A supplementary aim was to model the circumstellar activity in the system from K band spectral lines. Methods. The data used include interferometric observations from the VLTI instruments GRAVITY and PIONIER, as well as the MIRC-X instrument at the CHARA Array. We geometrically modelled the dust continuum to derive relative astrometry at 13 epochs, determine the orbital elements, and constrain individual stellar parameters at five different age estimates. We used the continuum models as a base to examine differential phases, visibilities, and closure phases over the Br γ and He I emission lines in order to characterise the nature of the circumstellar emission. Results. Our orbit solution suggests a period of P = 367.7 ± 0.1 d, approximately twice as long as found with previous radial velocity orbit fits. We derive a semi-major axis of 2.61 ± 0.04 au at d = 990 ± 50 pc, an eccentricity of 0.498 ± 0.001, and an orbital inclination of 53.6 ± 0.3°. This allowed the component masses to be constrained to M1 = 12.2 ± 2.2 M⊙ and M2 = 4.9 ± 0.5 M⊙. The line-emitting gas was found to be localised around the primary and is spatially resolved on scales of ∼11 stellar radii, where the spatial displacement between the line wings is consistent with a rotating disc. Conclusions. The large spatial extent and stable rotation axis orientation measured for the Br γ and He I line emission are inconsistent with an origin in magnetospheric accretion or boundary-layer accretion, but indicate an ionised inner gas disc around this Herbig Be star. We observe line variability that could be explained either with generic line variability in a Herbig star disc or V/R variations in a decretion disc scenario. We have also constrained the age of the system, with relative flux ratios suggesting an age of ∼(7 ± 2)×105 yr, consistent with the system being composed of a main-sequence primary and a secondary still contracting towards the main-sequence stage.

We report radial velocity (RV) measurements of the G-type subgiants 24 Sextanis (= HD 90043) and HD 200964.
\nBoth are massive, evolved stars that exhibit periodic variations due to the presence of a pair of Jovian planets.
\nPhotometric monitoring with the T12 0.80 m APT at Fairborn Observatory demonstrates both stars to be constant
\nin brightness to ≤ 0.002 mag, thus strengthening the planetary interpretation of the RV variations. Based on our
\ndynamical analysis of the RV time series, 24 Sex b, c have orbital periods of 452.8 days and 883.0 days, corresponding
\nto semimajor axes 1.333 AU and 2.08 AU, and minimum masses 1.99 M_(Jup) and 0.86 M_(Jup), assuming a stellar mass
\nM_⋆ =1.54 M_⊙. HD 200964 b, c have orbital periods of 613.8 days and 825.0 days, corresponding to semimajor axes
\n1.601 AU and 1.95 AU, and minimum masses 1.99 M_(Jup) and 0.90 M_(Jup), assuming M_⋆ = 1.44 M_⊙. We also carry
\nout dynamical simulations to properly account for gravitational interactions between the planets. Most, if not all,
\nof the dynamically stable solutions include crossing orbits, suggesting that each system is locked in a mean-motion
\nresonance that prevents close encounters and provides long-term stability. The planets in the 24 Sex system likely
\nhave a period ratio near 2:1, while the HD 200964 system is even more tightly packed with a period ratio close to
\n4:3. However, we caution that further RV observations and more detailed dynamical modeling will be required to
\nprovide definitive and unique orbital solutions for both cases, and to determine whether the two systems are truly
\nresonant.

Context. The occurrence rate and period distribution of (giant) planets around young stars is still not as well constrained as for older main-sequence stars. This is mostly due to the intrinsic activity-related complications and the avoidance of young stars in many large planet search programmes. Yet, dynamical restructuring processes in planetary systems may last significantly longer than the actual planet formation phase and may well extend long into the debris disc phase, such that the planet populations around young stars may differ from those observed around main-sequence stars. Aims. We introduce our Radial Velocity Survey for Planets around Young stars (RVSPY), which is closely related to the NaCo-ISPY direct imaging survey, characterise our target stars, and search for substellar companions at orbital separations smaller than a few au from the host star. Methods. We used the FEROS spectrograph, mounted to the MPG/ESO 2.2 m telescope in Chile, to obtain high signal-to-noise spectra and time series of precise radial velocities (RVs) of 111 stars, most of which are surrounded by debris discs. Our target stars have spectral types between early F and late K, a median age of 400 Myr, and a median distance of 45 pc. During the initial reconnaissance phase of our survey, we determined stellar parameters and used high-cadence observations to characterise the intrinsic stellar activity, searched for hot companions with orbital periods of up to 10 days, and derived the detection thresholds for longer-period companions. In our analysis we, have included archival spectroscopic data, spectral energy distribution, and data for photometric time series from the TESS mission. Results. For all target stars we determined their basic stellar parameters and present the results of the high-cadence RV survey and activity characterisation. We have achieved a median single-measurement RV precision of 6 m s−1 and derived the short-term intrinsic RV scatter of our targets (median 23 m s−1), which is mostly caused by stellar activity and decays with an age from >100 m s−1 at <20 Myr to <20 m s−1 at >500 Myr. We analysed time series periodograms of the high-cadence RV data and the shape of the individual cross-correlation functions. We discovered six previously unknown close companions with orbital periods between 10 and 100 days, three of which are low-mass stars, and three are in the brown dwarf mass regime. We detected no hot companion with an orbital period <10 days down to a median mass limit of ~1 MJup for stars younger than 500 Myr, which is still compatible with the established occurrence rate of such companions around main-sequence stars. We found significant RV periodicities between 1.3 and 4.5 days for 14 stars, which are, however, all caused by rotational modulation due to starspots. We also analysed the data for TESS photometric time series and found significant periodicities for most of the stars. For 11 stars, the photometric periods are also clearly detected in the RV data. We also derived stellar rotation periods ranging from 1 to 10 days for 91 stars, mostly from the TESS data. From the intrinsic activity-related short-term RV jitter, we derived the expected mass-detection thresholds for longer-period companions, and selected 84 targets for the longer-term RV monitoring.

WRF‐Var is further developed with Physical Initialization (PI) to assimilate Doppler radar radial velocity and reflectivity observations. In this updated 3D‐Var, specific humidity and vertical velocity are first derived from reflectivity with PI, and then the model fields of specific humidity are replaced by the modified ones, finally, the estimated vertical velocity is added to the cost‐function of the existing WRF‐Var (version 2.0) as a new observation type, and radial velocity observations are assimilated directly by the method afforded by WRF‐Var. It is tested with a rainfall event that occurred in Hubei province near the Yangtze River on 19 June 2002. Results show that the updated 3D‐Var shows better capability to forecast the precipitation than the WRF‐Var does, and the forecast reflectivity field correlates well with the observations for about 4‐h prediction period.

We present the identification of potential members of nearby Galactic globular clusters using radial velocities from the RAdial Velocity Experiment Data Release 4 (RAVE-DR4) survey database. Our identifications are based on three globular clusters -- NGC 3201, NGC 5139 ($\omega$ Cen) and NGC 362 -- all of which are shown to have |RV|>100 km/s. The identification of globular cluster stars in RAVE DR4 data offers a unique opportunity to test the precision and accuracy of the stellar parameters determined with the currently available Stellar Parameter Pipelines (SPPs) used in the survey, as globular clusters are ideal testbeds for the validation of stellar atmospheric parameters, abundances, distances and ages. For both NGC 3201 and $\omega$ Cen, there is compelling evidence for numerous members (> 10) in the RAVE database; in the case of NGC 362 the evidence is more ambiguous, and there may be significant foreground and/or background contamination in our kinematically-selected sample. A comparison of the RAVE-derived stellar parameters and abundances with published values for each cluster and with BASTI isochrones for ages and metallicities from the literature reveals overall good agreement, with the exception of the apparent underestimation of surface gravities for giants, in particular for the most metal-poor stars. Moreover, if the selected members are part of the main body of each cluster our results would also suggest that the distances from Binney et al. 2013, where only isochrones more metal-rich than -0.9 dex were used, are typically underestimated by ~ 40% with respect to the published distances for the clusters, while the distances from Zwitter et al. 2010 show stars ranging from 1 to ~ 6.5 kpc -- with indications of a trend toward higher distances at lower metallicities -- for the three clusters analysed in this study.

ABSTRACTRadial velocity searches for substellar‐mass companions have focused primarily on stars older than 1 Gyr. Increased levels of stellar activity in young stars hinders the detection of solar system analogs, and therefore until recently there has been a prejudice against inclusion of young stars in radial velocity surveys. Adaptive optics surveys of young stars have given us insight into the multiplicity of young stars, but only for massive, distant companions. Understanding the limit of the radial velocity technique, restricted to high‐mass, close‐orbiting planets and brown dwarfs, we began a survey of young stars of various ages. While the number of stars needed to carry out full analysis of the problems of planetary and brown dwarf population and evolution is large, the beginning of such a sample is included here. We report on 61 young stars ranging in age from the β Pictoris association (∼12 Myr) to the Ursa Major association (∼300 Myr). This initial search resulted in no stars showing evidence of companions larger than ∼1MJup–2MJup in short‐period orbits at the 3 σ level. We also present derived stellar parameters, as most have unpublished values. The chemical homogeneity of a cluster, and presumably of an association, may help to constrain true membership, so we present [Fe/H] abundances for the stars in our sample.

The Survey for Distant Solar Twins aims to find stars very similar to the Sun at distances of 1–$4\, {\rm kpc}$, several times more distant than any currently known solar twins and analogues. The goal is to identify the best stars with which to test whether the fine-structure constant, α, varies with dark matter density in our Galaxy. Here, we use epic, our line-by-line differential technique, to measure the stellar parameters – effective temperature Teff, surface gravity log g, and metallicity [Fe/H] – from moderate-resolution (R ≲ 32 000) spectra of 877 solar twin and analogue candidates (547 at 1–$4\, {\rm kpc}$) observed with the High Efficiency and Resolution Multi-Element Spectrograph (HERMES) on the Anglo-Australian Telescope. These are consistent with expectations for Teff and log g from photometry, and for [Fe/H] from the Besançon stellar population model. epic provides small enough uncertainties ($\sim 90\, {\rm K}$, $0.08\, {\rm dex}$, and $0.05\, {\rm dex}$, respectively), even at the low signal-to-noise ratios available (${\rm S/N}\gtrsim$ 25 per pixel), to identify 299 new solar analogues ($\ge 90~{{\ \rm per\ cent}}$ confidence) and 20 solar twins (≥50 per cent confidence), 206 and 12 of which are at 1–$4\, {\rm kpc}$. By extending epic to measure line broadening and lithium abundance from HERMES spectra, and with ages derived from isochrone fitting with our stellar parameters, we identify 174 solar analogues at 1–$4\, {\rm kpc}$ that are relatively inactive, slowly rotating, and with no evidence of spectroscopic binarity. These are the preferred targets for follow-up spectroscopy to measure α.

Context.Active regions on the photosphere of a star have been the major obstacle for detecting Earth-like exoplanets using the radial velocity (RV) method. A commonly employed solution for addressing stellar activity is to assume a linear relationship between the RV observations and the activity indicators along the entire time series, and then remove the estimated contribution of activity from the variation in RV data (overall correction method). However, since active regions evolve on the photosphere over time, correlations between the RV observations and the activity indicators will correspondingly be anisotropic.Aims.We present an approach that recognizes the RV locations where the correlations between the RV and the activity indicators significantly change in order to better account for variations in RV caused by stellar activity.Methods.The proposed approach uses a general family of statistical breakpoint methods, often referred to as change point detection (CPD) algorithms; several implementations of which are available in R and python. A thorough comparison is made between the breakpoint-based approach and the overall correction method. To ensure wide representativity, we use measurements from real stars that have different levels of stellar activity and whose spectra have different signal-to-noise ratios.Results.When the corrections for stellar activity are applied separately to each temporal segment identified by the breakpoint method, the corresponding residuals in the RV time series are typically much smaller than those obtained by the overall correction method. Consequently, the generalized Lomb–Scargle periodogram contains a smaller number of peaks caused by active regions. The CPD algorithm is particularly effective when focusing on active stars with long time series, such asαCen B. In that case, we demonstrate that the breakpoint method improves the detection limit of exoplanets by 74% on average with respect to the overall correction method.Conclusions.CPD algorithms provide a useful statistical framework for estimating the presence of change points in a time series. Since the process underlying the RV measurements generates anisotropic data by its intrinsic properties, it is natural to use CPD to obtain cleaner signals from RV data. We anticipate that the improved exoplanet detection limit may lead to a widespread adoption of such an approach. Our test on the HD 192310 planetary system is encouraging, as we confirm the presence of the two hosted exoplanets and we determine orbital parameters consistent with the literature, also providing much more precise estimates for HD 192310 c.

We announce the discovery of two planets orbiting the M dwarfs GJ 251 (0.360 ± 0.015M⊙) and HD 238090 (0.578 ± 0.021M⊙) based on CARMENES radial velocity (RV) data. In addition, we independently confirm with CARMENES data the existence of Lalande 21185 b, a planet that has recently been discovered with the SOPHIE spectrograph. All three planets belong to the class of warm or temperate super-Earths and share similar properties. The orbital periods are 14.24 d, 13.67 d, and 12.95 d and the minimum masses are 4.0 ± 0.4 M⊕, 6.9 ± 0.9 M⊕, and 2.7 ± 0.3 M⊕ for GJ 251 b, HD 238090 b, and Lalande 21185 b, respectively. Based on the orbital and stellar properties, we estimate equilibrium temperatures of 351.0 ± 1.4 K for GJ 251 b, 469.6 ± 2.6 K for HD 238090 b, and 370.1 ± 6.8 K for Lalande 21185 b. For the latter we resolve the daily aliases that were present in the SOPHIE data and that hindered an unambiguous determination of the orbital period. We find no significant signals in any of our spectral activity indicators at the planetary periods. The RV observations were accompanied by contemporaneous photometric observations. We derive stellar rotation periods of 122.1 ± 2.2 d and 96.7 ± 3.7 d for GJ 251 and HD 238090, respectively. The RV data of all three stars exhibit significant signals at the rotational period or its first harmonic. For GJ 251 and Lalande 21185, we also find long-period signals around 600 d, and 2900 d, respectively, which we tentatively attribute to long-term magnetic cycles. We apply a Bayesian approach to carefully model the Keplerian signals simultaneously with the stellar activity using Gaussian process regression models and extensively search for additional significant planetary signals hidden behind the stellar activity. Current planet formation theories suggest that the three systems represent a common architecture, consistent with formation following the core accretion paradigm.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation Johny Setiawan, Rainer Klement, Thomas Henning, Hans‐Walter Rix, Boyke Rochau, Tim Schulze‐Hartung, Jens Rodmann; A Planetary Companion around a Metal‐Poor Star with Extragalactic Origin. AIP Conf. Proc. 10 March 2011; 1331 (1): 182–189. https://doi.org/10.1063/1.3556200 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

A goal of the future Habitable Worlds Observatory (HWO) is to directly image and spectroscopically characterize true Earth-analogs. However, if a large fraction of HWO target stars host unknown dynamically disruptive giant planets in their habitable zones (HZs), then additional targets that are farther away will need to be surveyed, potentially requiring a larger-aperture telescope and a coronagraph with a smaller inner working angle. Therefore, the sooner we constrain the presence of massive planets orbiting potential HWO target stars, the easier and less costly it will be to adjust key aspects of HWO’s architecture. In this work, we uniformly analyze over 153,000 public radial velocity (RV) observations of 120 potential HWO target stars to derive mass limits on planetary companions. The RVs were measured by 23 spectrographs located at 15 observatories around the world, with the first observations going back to 1987. Based on empirical search completeness tests, we determine that undetected Jupiter-mass (Saturn-mass) planets may be hiding in up to 38% (53%) of the HZs of targets in the ExEP Mission Star List. The median mass sensitivity limit in the middle of the conservative HZ is approximately 48 M ⊕ . We also provide updated parameters for 53 known companions, and we detect at least 26 additional RV signals corresponding to stellar activity and 4 signals that are planet candidates. We note that 44 of the ExEP stars lack substantial RV monitoring history, and we advocate for community-coordinated observing campaigns of these stars using moderate-precision RV facilities.

Data from transit light curves, radial velocity, and transit timing observations can be used to probe the interiors of exoplanets beyond the mean density, by measuring the Love numbers h 2 and k 2. The first indirect estimate of k 2 for an exoplanet from radial velocity and transit timing variation observations has been performed by taking advantage of the years-spanning baseline. Not a single measurement of h 2 has been achieved from transit light curves, mostly because the photometric precision of current observing facilities is still too low. We show that the Imaging Spectrograph instrument onboard the Hubble Space Telescope (HST) could measure h 2 of the hot Jupiter WASP-121b if only a few more observations were gathered. We show that a careful treatment of the noise and stellar limb darkening (LD) must be carried out to achieve a measurement of h 2. In particular, we find that the impact of the noise modeling on the estimation of h 2 is stronger than that of the LD modeling. In addition, we emphasize that the wavelet method for correlated noise analysis can mask limb brightening. Finally, using currently available data, we briefly discuss the tentative measurement of in terms of interior structure. Additional observations would further constrain the interior of WASP-121b and possibly provide insights on the physics of inflation. The possibility of using the approach presented here with the HST provides a bridge before the high-quality data to be returned by the James Webb Space Telescope and PLATO telescope in the coming decade.

Photodynamical modeling of star systems using available Kepler transit photometry and radial velocity observations has provided unique constraints on physical parameters of stars, providing insight into stellar structure and formation models (Carter et al. 2011). The inclusion of forthcoming astrometric measurements from the ongoing ESA Gaia mission will help improve the accuracy and precision of these models by constraining the orbital motion of stars around the system barycenter in the plane of the sky. Here I use the self-developed Transit, Astrometry, and RV Fitter (TAR-Fit) photodynamical model to update the parameters of the KOI-126 system, first reported in Carter et al. (2011). KOI-126 is a triply-eclipsing stellar system composed of a low-mass binary in orbit around a solar-type star. I use a Bulirsch-Stoer numerical integrator written in C to compute the dynamics of the system in a heliocentric frame, and run a Markov Chain Monte Carlo fitting process calculating the chi-square value for the simulated transits, astrometry, and RV data produced by the integrator compared to observational data. The best-fit model parameters I calculated for the dataset from Carter et al. (2011) were consistent with their parameters, but not consistent with the full photometric dataset, and required slight tweaks in the orbital angles of the system in order to fit all the transits. The evolution of the parameters for KOI-126 throughout the 7 years of Kepler and radial velocity observations provides strong constraints on the best-fit parameter values.

The InfraRed Doppler (IRD) instrument is a high-dispersion spectrograph that is available on Subaru Telescope to explore extrasolar planets via infrared radial velocity (RV) observations. The Subaru/IRD is especially useful in the search of a low-mass planet around cool M-type dwarfs for which infrared RV observations are essential. We report our early performance tests for IRD. IRD’s two H2RG detectors have been evaluated with our detector readout technique, ensuring that their readout noise is made sufficiently smaller than the stellar photon noise expected in our planned survey. We have also tested the instrumental stability of RV measurements from the laboratory data obtained with the IRD’s calibration systems including a laser frequency comb (LFC). Among our tested three types of velocity stability, the stability of comb spectra obtained with a multi-mode fiber (MMF) relative to that with another MMF is measured to be ∼1 m s−1. We also infer from these tests that stellar RV measurements with an MMF can be calibrated with a short-term stability of 2 m s−1 or better by the simultaneously-observed reference spectra of LFC. Furthermore, we report preliminary on-sky RV measurements calibrated with a Thorium-Argon hollow-cathode lamp for RV-stable stars (τ Ceti and Barnard's star) and a planet-host (51 Pegasi). These preliminary RV measurements help the further performance test of IRD that will be performed by the on-sky observations with LFC.

Deriving orbital parameters and masses of extrasolar planets by means of measuring the variation of the host star positions requires an astrometric accuracy of 10 microarcsec. To achieve this goal, a consortium with partners from Germany, the Netherlands, and Switzerland, in agreement with ESO, will enhance the PRIMA facility at the VLTI with Differential Delay Lines (DDLs). We give an overview of the PRIMADDL project, which consists of developing hardware, astrometric operation tools, and data reduction software, and outline the anticipated astrometric planet search program to be carried out with this facility. 1 Narrow-angle Astrometry with the VLTI PRIMA, the instrument for Phase Referenced Imaging and Micro-arcsecond Astrometry is currently being developed at ESO. PRIMA will implement the dual-feed capability at the VLTI for both UTs and ATs to enable simultaneous interferometric observations of two objects that are separated by up to 1 arcmin, without requiring a large continuous field of view. PRIMA will be composed of four major sub-systems: Star Separators, Differential Delay Lines (DDLs), a laser metrology system, and Fringe Sensor Units (FSU). The system is designed to perform high-accuracy (10μas) narrow-angle differential astrometry in K-band with two FSUs and, with one FSU in combination with AMBER or MIDI, phase-referenced aperture synthesis imaging. The purpose of the DDLs in differential astrometry is to increase the astrometric accuracy by separating the large OPD correction terms which are common for the two stars from the small differential terms, and to increase the sensitivity by stabilizing the fringe pattern (in a closed loop with the laser metrology) and thus allow for longer integrations. 2 DDLs and Astrometric Software for PRIMA In order to speed up the full implementation of the 10μas astrometric capability of the VLTI and to carry out a large astrometric planet search program, a consortium lead by the Observatoire de Geneve (Switzerland), the Max Planck Institute for Astronomy in Heidelberg (Germany), and the University of Leiden/NOVA (The Netherlands) agreed with ESO to build and deliver the Differential Delay Lines for PRIMA (see Fig. 1) and to provide all necessary operation 266 Launhardt et al. and software tools to perform narrow-angle astrometry at the 10μas level. This includes developing and building all the DDL hardware, the construction and analysis of an astrometric error budget, the establishment of an operations and calibration strategy, and the development of observation preparation and data reduction software: Fig. 1. The PRIMA-DDL project: breakdown of hard and software components 3 The Astrometric Planet Search Program When completed in 2007, we will use the upgraded PRIMA facility to detect and characterize extra-solar planets through the reflex motions of their host stars in the plane of the sky. Two core programs are planned to be carried out over a duration of at least three years: 1) Observe all stars with known radial-velocity planets that are in reach of the VLTI and have a suitable phase reference star. We will resolve the sin i uncertainty of the planet masses and thus constrain the uncertain upper end of the planetary mass function. For stars with multiple planetary systems we will derive the relative inclination of the orbits. We will follow up long-term radial velocity trends and search for new planets in longer-period orbits for which astrometry is more sensitive than the radial velocity method. 2) Planet search around stars of different mass and evolutionary status without known planets. The search for planets by the radial-velocity technique is restricted to stars with narrow and stable spectral lines, thus excluding A and most F stars with their broad spectral lines as well as pre-main sequence stars. Our astrometric planet search program will explicitly include such stars. For nearby (< 20 pc) late-type (F-M) main sequence stars, the primary new discovery space opened by such an astrometric facility would be Saturn down to Uranus-mass planets with orbital periods of a few years (a = 1–5AU).