287 research outputs found
The [Y/Mg] clock works for evolved solar metallicity stars
Previously [Y/Mg] has been proven to be an age indicator for solar twins.
Here, we investigate if this relation also holds for helium-core-burning stars
of solar metallicity. High resolution and high signal-to-noise ratio (S/N)
spectroscopic data of stars in the helium-core-burning phase have been obtained
with the FIES spectrograph on the NOT 2.56m telescope and the HIRES
spectrograph on the Keck I 10 m telescope. They have been analyzed to determine
the chemical abundances of four open clusters with close to solar metallicity;
NGC 6811, NGC 6819, M67 and NGC 188. The abundances are derived from equivalent
widths of spectral lines using ATLAS9 model atmospheres with parameters
determined from the excitation and ionization balance of Fe lines. Results from
asteroseismology and binary studies were used as priors on the atmospheric
parameters, where especially the is determined to much higher
precision than what is possible with spectroscopy. It is confirmed that the
four open clusters are close to solar metallicity and they follow the [Y/Mg]
vs. age trend previously found for solar twins. The [Y/Mg] vs. age clock also
works for giant stars in the helium-core burning phase, which vastly increases
the possibilities to estimate the age of stars not only in the solar
neighborhood, but in large parts of the Galaxy, due to the brighter nature of
evolved stars compared to dwarfs.Comment: 5 pages, 3 figures, accepted for publication as a Letter to A&
Na I and H absorption features in the atmosphere of MASCARA-2b/KELT-20b
We have used the HARPS-North high resolution spectrograph (=115
000) at TNG to observe one transit of the highly irradiated planet
MASCARA-2b/KELT-20b. Using only one transit observation, we are able to clearly
resolve the spectral features of the atomic sodium (Na I) doublet and the
H line in its atmosphere, measuring absorption depths of
0.170.03 and 0.590.08 for a 0.75 passband,
respectively. These absorptions are corroborated with the transmission measured
from their respective transmission light curves, which show a large
Rossiter-McLaughlin effect. In case of H, this absorption corresponds
to an effective radius of =1.200.04. While the S/N of the
final transmission spectrum is not sufficient to adjust different temperature
profiles to the lines, we find that higher temperatures than the equilibrium
are needed to explain the lines contrast. Particularly, we find that the Na I
lines core require a temperature of T=4210180K and that H requires
T=4330520K. MASCARA-2b, like other planets orbiting A-type stars, receives
a large amount of UV energy from its host star. This energy excites the atomic
hydrogen and produces H absorption, leading to the expansion and
abrasion of the atmosphere. The study of other Balmer lines in the transmission
spectrum would allow the determination of the atmospheric temperature profile
and the calculation of the lifetime of the atmosphere. In the case of
MASCARA-2b, residual features are observed in the H and H lines,
but they are not statistically significant. More transit observations are
needed to confirm our findings in Na I and H, and to build up enough
S/N to explore the presence of H and H planetary absorptions.Comment: 14 pages, 12 figure
MASCARA-2 b: A hot Jupiter transiting the A-star HD185603
In this paper we present MASCARA-2 b, a hot Jupiter transiting the
A2 star HD 185603. Since early 2015, MASCARA has taken more than 1.6 million
flux measurements of the star, corresponding to a total of almost 3000 hours of
observations, revealing a periodic dimming in the flux with a depth of .
Photometric follow-up observations were performed with the NITES and IAC80
telescopes and spectroscopic measurements were obtained with the Hertzsprung
SONG telescope. We find MASCARA-2 b orbits HD 185603 with a period of
at a distance of , has a radius of and place a
upper limit on the mass of . HD 185603 is a
rapidly rotating early-type star with an effective temperature of
and a mass and radius of
, , respectively. Contrary
to most other hot Jupiters transiting early-type stars, the projected planet
orbital axis and stellar spin axis are found to be aligned with . The brightness of the host star and the high equilibrium
temperature, , of MASCARA-2 b make it a suitable target for
atmospheric studies from the ground and space. Of particular interest is the
detection of TiO, which has recently been detected in the similarly hot planets
WASP-33 b and WASP-19 b.Comment: 8 pages, 4 figures, Accepted for publication in A&
The K2-ESPRINT Project VI: K2-105 b, a Hot-Neptune around a Metal-rich G-dwarf
We report on the confirmation that the candidate transits observed for the
star EPIC 211525389 are due to a short-period Neptune-sized planet. The host
star, located in K2 campaign field 5, is a metal-rich ([Fe/H] = 0.260.05)
G-dwarf (T_eff = 543070 K and log g = 4.480.09), based on
observations with the High Dispersion Spectrograph (HDS) on the Subaru 8.2m
telescope. High-spatial resolution AO imaging with HiCIAO on the Subaru
telescope excludes faint companions near the host star, and the false positive
probability of this target is found to be < using the open source
vespa code. A joint analysis of transit light curves from K2 and additional
ground-based multi-color transit photometry with MuSCAT on the Okayama 1.88m
telescope gives the orbital period of P = 8.2669020.000070 days and
consistent transit depths of or . The transit depth corresponds to a planetary radius of , indicating that EPIC 211525389 b is a
short-period Neptune-sized planet. Radial velocities of the host star, obtained
with the Subaru HDS, lead to a 3\sigma\ upper limit of 90 on the mass of EPIC 211525389 b, confirming its planetary nature.
We expect this planet, newly named K2-105 b, to be the subject of future
studies to characterize its mass, atmosphere, spin-orbit (mis)alignment, as
well as investigate the possibility of additional planets in the system.Comment: 11 pages, 9 figures, 4 tables, PASJ accepte
The K2-ESPRINT Project. I. Discovery of the Disintegrating Rocky Planet K2-22b with a Cometary Head and Leading Tail
We present the discovery of a transiting exoplanet candidate in the K2
Field-1 with an orbital period of 9.1457 hr: K2-22b. The highly variable
transit depths, ranging from 0\% to 1.3\%, are suggestive of a planet
that is disintegrating via the emission of dusty effluents. We characterize the
host star as an M-dwarf with K. We have obtained
ground-based transit measurements with several 1-m class telescopes and with
the GTC. These observations (1) improve the transit ephemeris; (2) confirm the
variable nature of the transit depths; (3) indicate variations in the transit
shapes; and (4) demonstrate clearly that at least on one occasion the transit
depths were significantly wavelength dependent. The latter three effects tend
to indicate extinction of starlight by dust rather than by any combination of
solid bodies. The K2 observations yield a folded light curve with lower time
resolution but with substantially better statistical precision compared with
the ground-based observations. We detect a significant "bump" just after the
transit egress, and a less significant bump just prior to transit ingress. We
interpret these bumps in the context of a planet that is not only likely
streaming a dust tail behind it, but also has a more prominent leading dust
trail that precedes it. This effect is modeled in terms of dust grains that can
escape to beyond the planet's Hill sphere and effectively undergo `Roche lobe
overflow,' even though the planet's surface is likely underfilling its Roche
lobe by a factor of 2.Comment: 22 pages, 16 figures. Final version accepted to Ap
EPIC 219388192 b - an inhabitant of the brown dwarf desert in the Ruprecht 147 open cluster
We report the discovery of EPIC 219388192 b, a transiting brown dwarf in a
5.3-day orbit around a member star of Ruprecht-147, the oldest nearby open
cluster association, which was photometrically monitored by K2 during its
Campaign 7. We combine the K2 time-series data with ground-based adaptive
optics imaging and high resolution spectroscopy to rule out false positive
scenarios and determine the main parameters of the system. EPIC 219388192 b has
a radius of =~ and mass of
=~, yielding a mean density of
~. The host star is nearly a Solar twin with
mass =~, radius
=~, effective temperature
=~K and iron abundance [Fe/H]=~dex.
Its age, spectroscopic distance, and reddening are consistent with those of
Ruprecht-147, corroborating its cluster membership. EPIC 219388192 b is the
first brown dwarf with precise determinations of mass, radius and age, and
serves as benchmark for evolutionary models in the sub-stellar regime.Comment: 13 pages, 11 figures, 4 tables, submitted to AAS Journal
K2-137 b: an Earth-sized planet in a 4.3-hour orbit around an M-dwarf
We report the discovery from K2 of a transiting terrestrial planet in an
ultra-short-period orbit around an M3-dwarf. K2-137 b completes an orbit in
only 4.3 hours, the second-shortest orbital period of any known planet, just 4
minutes longer than that of KOI 1843.03, which also orbits an M-dwarf. Using a
combination of archival images, AO imaging, RV measurements, and light curve
modelling, we show that no plausible eclipsing binary scenario can explain the
K2 light curve, and thus confirm the planetary nature of the system. The
planet, whose radius we determine to be 0.89 +/- 0.09 Earth radii, and which
must have a iron mass fraction greater than 0.45, orbits a star of mass 0.463
+/- 0.052 Msol and radius 0.442 +/- 0.044 Rsol.Comment: 12 pages, 9 figures, accepted for publication in MNRA
HD 191939 revisited: New and refined planet mass determinations, and a new planet in the habitable zone
HD 191939 (TOI-1339) is a nearby (d=54pc), bright (V=9mag), and inactive
Sun-like star (G9 V) known to host a multi-planet transiting system.
Ground-based spectroscopic observations confirmed the planetary nature of the
three transiting sub-Neptunes (HD 191939 b, c, and d) originally detected by
TESS and were used to measure the masses for planets b and c with 3
precision. These previous observations also reported the discovery of an
additional Saturn-mass planet (HD 191939 e) and evidence for a further, very
long-period companion (HD 191939 f). Here, we report the discovery of a new
non-transiting planet in the system and a refined mass determination of HD
191939 d. The new planet, HD 191939 g, has a minimum mass of 13.52.0
M and a period of about 280 d. This period places the planet within
the conservative habitable zone of the host star, and near a 1:3 resonance with
HD 191939 e. The compilation of 362 radial velocity measurements with a
baseline of 677 days from four different high-resolution spectrographs also
allowed us to refine the properties of the previously known planets, including
a 4.6 mass determination for planet d, for which only a 2 upper
limit had been set until now. We confirm the previously suspected low density
of HD 191939 d, which makes it an attractive target for attempting atmospheric
characterisation. Overall, the planetary system consists of three sub-Neptunes
interior to a Saturn-mass and a Uranus-mass planet plus a high-mass long-period
companion. This particular configuration has no counterpart in the literature
and makes HD 191939 an exceptional multi-planet transiting system with an
unusual planet demographic worthy of future observation.Comment: Accepted for publication in A&A. 20 pages, 8 figure
HD 191939 revisited: New and refined planet mass determinations, and a new planet in the habitable zone
HD 191939 (TOI-1339) is a nearby (d = 54 pc), bright (V = 9 mag), and inactive Sun-like star (G9 V) known to host a multi-planet transiting system. Ground-based spectroscopic observations confirmed the planetary nature of the three transiting sub-Neptunes (HD 191939 b, c, and d) originally detected by TESS and were used to measure the masses for planets b and c with 3\ucf precision. These previous observations also reported the discovery of an additional Saturn-mass planet (HD 191939 e) and evidence for a further, very long-period companion (HD 191939 f). Here, we report the discovery of a new non-transiting planet in the system and a refined mass determination of HD 191939 d. The new planet, HD 191939 g, has a minimum mass of 13.5\ub12.0 M- and a period of about 280 days. This period places the planet within the conservative habitable zone of the host star, and near a 1:3 resonance with HD 191939 e. The compilation of 362 radial velocity measurements with a baseline of 677 days from four different high-resolution spectrographs also allowed us to refine the properties of the previously known planets, including a 4.6\ucf mass determination for planet d, for which only a 2\ucf upper limit had been set until now. We confirm the previously suspected low density of HD 191939 d, which makes it an attractive target for attempting atmospheric characterisation. Overall, the planetary system consists of three sub-Neptunes interior to a Saturn-mass and a Uranus-mass planet plus a high-mass long-period companion. This particular configuration has no counterpart in the literature and makes HD 191939 an exceptional multi-planet transiting system with an unusual planet demographic worthy of future observation
The low density, hot Jupiter TOI-640 b is on a polar orbit
TOI-640 b is a hot, puffy Jupiter with a mass of M
and radius of R, orbiting a slightly evolved F-type
star with a separation of R. Through
spectroscopic in-transit observations made with the HARPS spectrograph, we
measured the Rossiter-McLaughlin effect, analysing both in-transit radial
velocities and the distortion of the stellar spectral lines. From these
observations, we find the host star to have a projected obliquity of
. From the TESS light curve, we measured the stellar
rotation period, allowing us to determine the stellar inclination,
, meaning we are viewing the star pole-on. Combining
this with the orbital inclination allowed us to calculate the host star
obliquity, . TOI-640 b joins a group of planets orbiting
over stellar poles within the range . The origin of this
orbital configuration is not well understood.Comment: 15 pages, 12 figures, accepted for publication in A&A, in pres
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