| 1. |
- Boyajian, T., et al.
(författare)
-
Stellar diameters and temperatures - VI. High angular resolution measurements of the transiting exoplanet host stars HD 189733 and HD 209458 and implications for models of cool dwarfs
- 2015
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 447:1, s. 846-857
-
Tidskriftsartikel (refereegranskat)abstract
- We present direct radii measurements of the well-known transiting exoplanet host stars HD 189733 and HD 209458 using the CHARA Array interferometer. We find the limb-darkened angular diameters to be thetaLD = 0.3848 +/- 0.0055 and 0.2254 +/- 0.0072 milliarcsec for HD 189733 and HD 209458, respectively. HD 189733 and HD 209458 are currently the only two transiting exoplanet systems where detection of the respective planetary companion's orbital motion from high resolution spectroscopy has revealed absolute masses for both star and planet. We use our new measurements together with the orbital information from radial velocity and photometric time series data, Hipparcos distances, and newly measured bolometric fluxes to determine the stellar effective temperatures (Teff = 4875 +/- 43, 6093 +/- 103 K), stellar linear radii (R* = 0.805 +/- 0.016, 1.203 +/- 0.061 Rsun), mean stellar densities (rho* = 1.62 +/- 0.11, 0.58 +/- 0.14 rhosun), planetary radii (Rp = 1.216 +/- 0.024, 1.451 +/- 0.074 RJup), and mean planetary densities (rhop = 0.605 +/- 0.029, 0.196 +/- 0.033 rhoJup) for HD 189733 b and HD 209458 b, respectively. The stellar parameters for HD 209458, a F9 dwarf, are consistent with indirect estimates derived from spectroscopic and evolutionary modeling. However, we find that models are unable to reproduce the observational results for the K2 dwarf, HD 189733. We show that, for stellar evolutionary models to match the observed stellar properties of HD 189733, adjustments lowering the solar-calibrated mixing length parameter from 1.83 to 1.34 need to be employed.
|
|
| 2. |
- Eisner, N. L., et al.
(författare)
-
Planet Hunters Tess I: TOI 813, a subgiant hosting a transiting Saturn-sized planet on an 84-day orbit
- 2020
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 494:1, s. 750-763
-
Forskningsöversikt (refereegranskat)abstract
- We report on the discovery and validation of TOI 813 b (TIC55525572b), a transiting exoplanet identified by citizen scientists in data from NASA's Transiting Exoplanet Survey Satellite (TESS) and the first planet discovered by the Planet Hunters TESS project. The host star is a bright (V = 10.3 mag) subgiant (R* = 1.94 R☉, M☉ = 1.32 M☉). It was observed almost continuously by TESS during its first year of operations, during which time four individual transit events were detected. The candidate passed all the standard light curve-based vetting checks, and ground-based follow-up spectroscopy and speckle imaging enabled us to place an upper limit of 2 MJup (99 per cent confidence) on the mass of the companion, and to statistically validate its planetary nature. Detailed modelling of the transits yields a period of 83.8911+0.0027-0.0031 d, a planet radius of 6.71 ± 0.38 R⊕ and a semimajor axis of 0.423+0031-0.037 AU. The planet's orbital period combined with the evolved nature of the host star places this object in a relatively underexplored region of parameter space. We estimate that TOI 813 b induces a reflex motion in its host star with a semi-amplitude of ∼6 m s−1, making this a promising system to measure the mass of a relatively long-period transiting planet.
|
|
| 3. |
- Creevey, O. L., et al.
(författare)
-
Fundamental properties of the Population II fiducial stars HD 122563 and Gmb 1830 from CHARA interferometric observations
- 2012
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 545, s. A17-
-
Tidskriftsartikel (refereegranskat)abstract
- We have determined the angular diameters of two metal-poor stars, HD 122563 and Gmb 1830, using CHARA and Palomar Testbed Interferometer observations. For the giant star HD 122563, we derive an angular diameter theta(3D) = 0.940 +/- 0.011 milliarcseconds (mas) using limb-darkening from 3D convection simulations and for the dwarf star Gmb 1830 (HD 103095) we obtain a 1D limb-darkened angular diameter theta(1D) = 0.679 +/- 0.007 mas. Coupling the angular diameters with photometry yields effective temperatures with precisions better than 55 K (T-eff = 4598 +/- 41 K and 4818 +/- 54 K - for the giant and the dwarf star, respectively). Including their distances results in very well-determined luminosities and radii (L = 230 +/- 7 L-circle dot, R = 24.1 +/- 1.1 R-circle dot and L = 0.213 +/- 0.002 L-circle dot, R = 0.665 +/- 0.014 R-circle dot, respectively). We used the CESAM2k stellar structure and evolution code in order to produce models that fit the observational data. We found values of the mixing-length parameter alpha (which describes 1D convection) that depend on the mass of the star. The masses were determined from the models with precisions of < 3% and with the well-measured radii excellent constraints on the surface gravity are obtained (log g = 1.60 +/- 0.04, 4.59 +/- 0.02 dex, respectively). The very small errors on both log g and T-eff provide stringent constraints for spectroscopic analyses given the sensitivity of abundances to both of these values. The precise determination of T-eff for the two stars brings into question the photometric scales for metal-poor stars.
|
|
| 4. |
- Creevey, O. L., et al.
(författare)
-
Benchmark stars for Gaia Fundamental properties of the Population II star HD 140283 from interferometric, spectroscopic, and photometric data
- 2015
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 575
-
Tidskriftsartikel (refereegranskat)abstract
- Metal-poor halo stars are important astrophysical laboratories that allow us to unravel details about many aspects of astrophysics, including the chemical conditions at the formation of our Galaxy, understanding the processes of diffusion in stellar interiors, and determining precise effective temperatures and calibration of colour-effective temperature relations. To address any of these issues the fundamental properties of the stars must first be determined. HD140283 is the closest and brightest metal-poor Population II halo star (distance = 58 pc and V = 7.21), an ideal target that allows us to approach these questions, and one of a list of 34 benchmark stars defined for Gaia astrophysical parameter calibration. In the framework of characterizing these benchmark stars, we determined the fundamental properties of HD140283 (radius, mass, age, and effective temperature) by obtaining new interferometric and spectroscopic measurements and combining them with photometry from the literature. The interferometric measurements were obtained using the visible interferometer VEGA on the CHARA array and we determined a 1D limb-darkened angular diameter of theta(1D) = 0.353 +/- 0.013 milliarcsec. Using photometry from the literature we derived the bolometric flux in two ways: a zero reddening solution (A(V) = 0.0 mag) of F-bol of 3.890 +/- 0.066 x 10(-8) erg s(-1) cm(-2),and a maximum of A(V) = 0.1 mag solution of 4.220 +/- 0.067 x 10(-8) erg s(-1) cm(-2). The interferometric T-eff is thus between 5534 +/- 103 K and 5647 +/- 105 K and its radius is R = 2.21 +/- 0.08 R-circle dot. Spectroscopic measurements of HD140283 were obtained using HARPS, NARVAL, and UVES and a 1D LTE analysis of Ha line wings yielded T-effspec = 5626 +/- 75 K. Using fine-tuned stellar models including diffusion of elements we then determined the mass M and age t of HD140283. Once the metallicity has been fixed, the age of the star depends on M, initial helium abundance Y-i, and mixing-length parameter alpha, only two of which are independent. We derive simple equations to estimate one from the other two. We need to adjust a to much lower values than the solar one (similar to 2) in order to fit the observations, and if A(V) = 0.0 mag then 0.5 <= alpha <= 1. We give an equation to estimate t from M, Y-i (alpha), and A(V). Establishing a reference alpha = 1.00 and adopting Y-i = 0.245 we derive a mass and age of HD140283: M = 0.780 +/- 0.010 M-circle dot and t = 13.7 +/- 0.7 Gyr (A(V) = 0.0 mag), or M = 0.805 +/- 0.010 M-circle dot and t = 12.2 +/- 0.6 Gyr (A(V) = 0.1 mag). Our stellar models yield an initial (interior) metal-hydrogen mass fraction of [Z/X](i) = -1.70 and log g = 3.65 +/- 0.03. Theoretical advances allowing us to impose the mixing-length parameter would greatly improve the redundancy between M, Y-i, and age, while from an observational point of view, accurate determinations of extinction along with asteroseismic observations would provide critical information allowing us to overcome the current limitations in our results.
|
|
