Abstract
Given their location on the Hertzsprung-Russell (H-R) diagram, thoroughly characterized subgiant stars can place stringent constraints on a wide range of astrophysical problems. Accordingly, ...they are prime asteroseismic targets for the Transiting Exoplanet Survey Satellite (TESS) mission. In this work, we infer stellar properties for a sample of 347 subgiants located in the TESS Continuous Viewing Zones, which we select based on their likelihood of showing asteroseismic oscillations. We investigate how well they can be characterized using classical constraints (photometry, astrometry) and validate our results using spectroscopic values. We derive luminosities, effective temperatures, and radii with mean 1
σ
random (systematic) uncertainties of 4.5% (2%), 33 K (60 K), and 2.2% (2%), as well as more model-dependent quantities such as surface gravities, masses, and ages. We use our sample to demonstrate that subgiants are ideal targets for mass and age determination based on H-R diagram location alone, discuss the advantages of stellar parameters derived from a detailed characterization over widely available catalogs, show that the generally used 3D extinction maps tend to overestimate the extinction for nearby stars (distance ≲500 pc), and find a correlation that supports the rotation–activity connection in post-main-sequence stars. The complementary roles played by classical and asteroseismic data sets will open a window to unprecedented astrophysical studies using subgiant stars.
Abstract
We present analytic estimates of the fractional uncertainties on the mass, radius, surface gravity, and density of a transiting planet, using only empirical or semi-empirical measurements. ...We first express these parameters in terms of transit photometry and radial velocity (RV) observables, as well as the stellar radius
R
⋆
, if required. In agreement with previous results, we find that, assuming a circular orbit, the surface gravity of the planet (
g
p
) depends only on empirical transit and RV parameters, namely the planet period
P
, the transit depth
δ
, the RV semi-amplitude
K
⋆
, the transit duration
T
, and the ingress/egress duration
τ
. However, the planet mass and density depend on all these quantities, plus
R
⋆
. Thus, an inference about the planet mass, radius, and density must rely upon an external constraint such as the stellar radius. For bright stars, stellar radii can now be measured nearly empirically by using measurements of the stellar bolometric flux, the effective temperature, and the distance to the star via its parallax, with the extinction
A
V
being the only free parameter. For any given system, there is a hierarchy of achievable precisions on the planetary parameters, such that the planetary surface gravity is more accurately measured than the density, which in turn is more accurately measured than the mass. We find that surface gravity provides a strong constraint on the core mass fraction of terrestrial planets. This is useful, given that the surface gravity may be one of the best measured properties of a terrestrial planet.
A Catalog of M-dwarf Flares with ASAS-SN Rodríguez Martínez, Romy; Lopez, Laura A.; Shappee, Benjamin J. ...
The Astrophysical journal,
04/2020, Letnik:
892, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We analyzed the light curves of 1376 early-to-late, nearby M dwarfs to search for white-light flares using photometry from the All-Sky Automated Survey for Supernovae. We identified 480 M dwarfs with ...at least one potential flare employing a simple statistical algorithm that searches for sudden increases in V-band flux. After more detailed evaluation, we identified 62 individual flares on 62 stars. The event amplitudes range from mag. Using classical flare models, we place lower limits on the flare energies and obtain V-band energies spanning erg. The fraction of flaring stars increases with spectral type, and most flaring stars show moderate to strong H emission. Additionally, we find that 14 of the 62 flaring stars are rotational variables, and they have shorter rotation periods and stronger H emission than nonflaring rotational variable M dwarfs.
Abstract
We investigate and compare the composition of M-dwarf planets in systems with only one known planet (“singles”) to those residing in multiplanet systems (“multis”) and the fundamental ...properties of their host stars. We restrict our analysis to planets with directly measured masses and radii, which comprise a total of 70 planets: 30 singles and 40 multis in 19 systems. We compare the bulk densities for the full sample, which includes planets ranging in size from 0.52
R
⊕
to 12.8
R
⊕
, and find that single planets have significantly lower densities on average than multis, which we cannot attribute to selection biases. We compare the bulk densities normalized by an Earth model for planets with
R
p
< 6
R
⊕
and find that multis are also denser with 99% confidence. We calculate and compare the core/water mass fractions (CMF/WMF) of low-mass planets (
M
p
< 10
M
⊕
) and find that the likely rocky multis (with
R
p
< 1.6
R
⊕
) have lower CMFs than singles. We also compare the Fe/H metallicity and rotation period of all single-planet versus multiplanet host stars with such measurements in the literature and find that multiplanet hosts are significantly more metal-poor than those hosting a single planet. Moreover, we find that the host star metallicity decreases with increasing planet multiplicity. In contrast, we find only a modest difference in the rotation period. The significant differences in planetary composition and metallicity of the host stars point to different physical processes governing the formation of single-planet and multiplanet systems in M dwarfs.
ABSTRACT
TOI-1259 consists of a transiting exoplanet orbiting a main-sequence star, with a bound outer white dwarf (WDs) companion. Less than a dozen systems with this architecture are known. We ...conduct follow-up spectroscopy on the WD TOI-1259B using the Large Binocular Telescope to better characterize it. We observe only strong hydrogen lines, making TOI-1259B a DA WD. We see no evidence of heavy element pollution, which would have been evidence of planetary material around the WD. Such pollution is seen in $\sim 25{-}50{{\ \rm per\ cent}}$ of WDs, but it is unknown if this rate is higher or lower in TOI-1259-like systems that contain a known planet. Our spectroscopy permits an improved WD age measurement of $4.05^{+1.00}_{-0.42}$ Gyr, which matches gyrochronology of the main-sequence star. This is the first of an expanded sample of similar binaries that will allow us to calibrate these dating methods and provide a new perspective on planets in binaries.
Abstract
Lava worlds are a potential emerging population of Super-Earths that are on close-in orbits around their host stars, with likely partially molten mantles. To date, few studies have addressed ...the impact of magma on the observed properties of a planet. At ambient conditions, magma is less dense than solid rock; however, it is also more compressible with increasing pressure. Therefore, it is unclear how large-scale magma oceans affect planet observables, such as bulk density. We update
ExoPlex
, a thermodynamically self-consistent planet interior software, to include anhydrous, hydrous (2.2 wt% H
2
O), and carbonated magmas (5.2 wt% CO
2
). We find that Earth-like planets with magma oceans larger than ∼1.5
R
⊕
and ∼3.2
M
⊕
are modestly denser than an equivalent-mass solid planet. From our model, three classes of mantle structures emerge for magma ocean planets: (1) a mantle magma ocean, (2) a surface magma ocean, and (3) one consisting of a surface magma ocean, a solid rock layer, and a basal magma ocean. The class of planets in which a basal magma ocean is present may sequester dissolved volatiles on billion-year timescales, in which a 4
M
⊕
mass planet can trap more than 130 times the mass of water than in Earth’s present-day oceans and 1000 times the carbon in the Earth’s surface and crust.
Abstract
We present a reanalysis of the K2-106 transiting planetary system, with a focus on the composition of K2-106b, an ultra-short-period, super-Mercury candidate. We globally model existing ...photometric and radial velocity data and derive a planetary mass and radius for K2-106b of
M
p
= 8.53 ± 1.02
M
⊕
and
R
p
=
1.71
−
0.057
+
0.069
R
⊕
, which leads to a density of
ρ
p
=
9.4
−
1.5
+
1.6
g cm
−3
, a significantly lower value than previously reported in the literature. We use planet interior models that assume a two-layer planet comprised of a liquid, pure Fe core and an iron-free, MgSiO
3
mantle, and we determine that the range of the core mass fractions are consistent with the observed mass and radius. We use existing high-resolution spectra of the host star to derive the Fe/Mg/Si abundances (Fe/H = −0.03 ± 0.01, Mg/H = 0.04 ± 0.02, Si/H = 0.03 ± 0.06) to infer the composition of K2-106b. We find that K2-106b has a density and core mass fraction (
44
−
15
+
12
%
) consistent with that of Earth (CMF
⊕
= 32%). Furthermore, its composition is consistent with what is expected, assuming that it reflects the relative refractory abundances of its host star. K2-106b is therefore unlikely to be a super-Mercury, as has been suggested in previous literature.
ABSTRACT
A gold standard for the study of M dwarfs is the eclipsing binary CM Draconis. It is rare because it is bright (Jmag = 8.5) and contains twin fully convective stars on an almost perfectly ...edge-on orbit. Both masses and radii were previously measured to better than 1 per cent precision, amongst the best known. We use 15 sectors of data from the Transiting Exoplanet Survey Satellite (TESS) to show that CM Draconis is the gift that keeps on giving. Our paper has three main components. First, we present updated parameters, with radii and masses constrained to previously unheard-of precisions of ≈0.06 and ≈0.12 per cent, respectively. Secondly, we discover strong and variable spot modulation, suggestive of spot clustering and an activity cycle of the order of ≈4 yr. Thirdly, we discover 163 flares. We find a relationship between the spot modulation and flare rate, with flares more likely to occur when the stars appear brighter. This may be due to a positive correlation between flares and the occurrence of bright spots (plages). The flare rate is surprisingly not reduced during eclipse, but one flare may show evidence of being occulted. We suggest that the flares may be preferentially polar, which has positive implications for the habitability of planets orbiting M dwarfs.
We present moderate resolution near-infrared spectra in the H, J, and K band of M-dwarf hosts to candidate transiting exoplanets discovered by NASA's K2 mission. We employ known empirical ...relationships between spectral features and physical stellar properties to measure the effective temperature, radius, metallicity, and luminosity of our sample. Out of an initial sample of 56 late-type stars in K2, we identify 35 objects as M dwarfs. For that subsample, we derive temperatures ranging from 2870 to 4187 K, radii of 0.09-0.83 R , luminosities of , and Fe/H metallicities between −0.49 and 0.51 dex. We then employ the stellar properties derived from spectra, in tandem with the K2 light curves, to characterize their planets. We report 33 exoplanet candidates with orbital periods ranging from 0.19 to 21.16 days, and median radii and equilibrium temperatures of 2.3 R⊕ and 986 K, respectively. Using planet mass-radius relationships from the literature, we identify seven exoplanets as potentially rocky, although we conclude that probably none reside in the habitable zone of their parent stars.
ABSTRACT
M-dwarfs are the most abundant stars in the galaxy and popular targets for exoplanet searches. However, their intrinsic faintness and complex spectra inhibit precise characterization. We ...only know of dozens of M-dwarfs with fundamental parameters of mass, radius, and effective temperature characterized to better than a few per cent. Eclipsing binaries remain the most robust means of stellar characterization. Here we present two targets from the Eclipsing Binary Low Mass (EBLM) survey that were observed with K2: EBLM J0055-00 and EBLM J2217-04. Combined with HARPS and CORALIE spectroscopy, we measure M-dwarf masses with precisions better than 5 per cent, radii better than 3 per cent, and effective temperatures on order 1 per cent. However, our fits require invoking a model to derive parameters for the primary star and fitting the M-dwarf using the transit and radial velocity observations. By investigating three popular stellar models, we determine that the model uncertainty in the primary star is of similar magnitude to the statistical uncertainty in the model fits of the secondary M-dwarf. Therefore, whilst these can be considered benchmark M-dwarfs, we caution the community to consider model uncertainty when pushing the limits of precise stellar characterization.
PDF
