We present the confirmation of a new sub-Neptune close to the transition between super-Earths and sub-Neptunes transiting the M2 dwarf TOI-269 (TIC 220 479 565,
V
= 14.4 mag,
J
= 10.9 mag,
R
⋆
= ...0.40
R
⊙
,
M
⋆
= 0.39
M
⊙
,
d
= 57 pc). The exoplanet candidate has been identified in multiple TESS sectors, and validated with high-precision spectroscopy from HARPS and ground-based photometric follow-up from ExTrA and LCO-CTIO. We determined mass, radius, and bulk density of the exoplanet by jointly modeling both photometry and radial velocities with
juliet
. The transiting exoplanet has an orbital period of
P
= 3.6977104 ± 0.0000037 days, a radius of 2.77 ± 0.12
R
⊕
, and a mass of 8.8 ± 1.4
M
⊕
. Since TOI-269 b lies among the best targets of its category for atmospheric characterization, it would be interesting to probe the atmosphere of this exoplanet with transmission spectroscopy in order to compare it to other sub-Neptunes. With an eccentricity
e
= 0.425
−0.086
+0.082
, TOI-269 b has one of the highest eccentricities of the exoplanets with periods less than 10 days. The star being likely a few Gyr old, this system does not appear to be dynamically young. We surmise TOI-269 b may have acquired its high eccentricity as it migrated inward through planet-planet interactions.
We report the discovery and characterization of the transiting extrasolar planet TOI-1710 b. It was first identified as a promising candidate by the Transiting Exoplanet Survey Satellite. Its ...planetary nature was then established with SOPHIE and HARPS-N spectroscopic observations via the radial-velocity method. The stellar parameters for the host star are derived from the spectra and a joint Markov chain Monte-Carlo adjustment of the spectral energy distribution and evolutionary tracks of TOI-1710. A joint MCMC analysis of the TESS light curve and the radial-velocity evolution allows us to determine the planetary system properties. From our analysis, TOI-1710 b is found to be a massive warm super-Neptune (
M
p
= 28.3 ± 4.7
M
⊕
and
R
p
= 5.34 ± 0.11
R
⊕
) orbiting a G5V dwarf star (
T
eff
= 5665 ± 55 K) on a nearly circular 24.3-day orbit (
e
= 0.16 ± 0.08). The orbital period of this planet is close to the estimated rotation period of its host star
P
rot
= 22.5 ± 2.0 days and it has a low Keplerian semi-amplitude
K
= 6.4 ± 1.0 m s
−1
; we thus performed additional analyses to show the robustness of the retrieved planetary parameters. With a low bulk density of 1.03 ± 0.23 g cm
−3
and orbiting a bright host star (
J
= 8.3,
V
= 9.6), TOI-1710 b is one of the best targets in this mass-radius range (near the Neptunian desert) for atmospheric characterization via transmission spectroscopy, a key measurement in constraining planet formation and evolutionary models of sub-Jovian planets.
TESS first look at evolved compact pulsators Charpinet, S.; Brassard, P.; Fontaine, G. ...
Astronomy and astrophysics (Berlin),
12/2019, Letnik:
632
Journal Article, Web Resource
Recenzirano
Odprti dostop
Context.
The TESS satellite was launched in 2018 to perform high-precision photometry from space over almost the whole sky in a search for exoplanets orbiting bright stars. This instrument has opened ...new opportunities to study variable hot subdwarfs, white dwarfs, and related compact objects. Targets of interest include white dwarf and hot subdwarf pulsators, both carrying high potential for asteroseismology.
Aims.
We present the discovery and detailed asteroseismic analysis of a new
g
-mode hot B subdwarf (sdB) pulsator, EC 21494−7018 (TIC 278659026), monitored in TESS first sector using 120-s cadence.
Methods.
The TESS light curve was analyzed with standard prewhitening techniques, followed by forward modeling using our latest generation of sdB models developed for asteroseismic investigations. By simultaneously best-matching all the observed frequencies with those computed from models, we identified the pulsation modes detected and, more importantly, we determined the global parameters and structural configuration of the star.
Results.
The light curve analysis reveals that EC 21494−7018 is a sdB pulsator counting up to 20 frequencies associated with independent
g
-modes. The seismic analysis singles out an optimal model solution in full agreement with independent measurements provided by spectroscopy (atmospheric parameters derived from model atmospheres) and astrometry (distance evaluated from
Gaia
DR2 trigonometric parallax). Several key parameters of the star are derived. Its mass (0.391 ± 0.009
M
⊙
) is significantly lower than the typical mass of sdB stars and suggests that its progenitor has not undergone the He-core flash; therefore this progenitor could originate from a massive (≳2
M
⊙
) red giant, which is an alternative channel for the formation of sdBs. Other derived parameters include the H-rich envelope mass (0.0037 ± 0.0010
M
⊙
), radius (0.1694 ± 0.0081
R
⊙
), and luminosity (8.2 ± 1.1
L
⊙
). The optimal model fit has a double-layered He+H composition profile, which we interpret as an incomplete but ongoing process of gravitational settling of helium at the bottom of a thick H-rich envelope. Moreover, the derived properties of the core indicate that EC 21494−7018 has burnt ∼43% (in mass) of its central helium and possesses a relatively large mixed core (
M
core
= 0.198 ± 0.010
M
⊙
), in line with trends already uncovered from other g-mode sdB pulsators analyzed with asteroseismology. Finally, we obtain for the first time an estimate of the amount of oxygen (in mass;
X
(O)
core
= 0.16
+0.13
−0.05
) produced at this stage of evolution by an helium-burning core. This result, along with the core-size estimate, is an interesting constraint that may help to narrow down the still uncertain
12
C(
α
,
γ
)
16
O nuclear reaction rate.
We present the detection of three exoplanets orbiting the early M dwarf TOI-663 (TIC 54962195; V = 13.7 mag, J = 10.4 mag, R ★ = 0.512 ± 0.015 R ⊙ , M ★ = 0.514 ± 0.012 M ⊙ , d = 64 pc). TOI-663 b, ...c, and d, with respective radii of 2.27 ± 0.10 R ⊕ , 2.26 ± 0.10 R ⊕ , and 1.92 ± 0.13 R ⊕ and masses of 4.45 ± 0.65 M ⊕ , 3.65 ± 0.97 M ⊕ , and <5.2 M ⊕ at 99%, are located just above the radius valley that separates rocky and volatile-rich exoplanets. The planet candidates are identified in two TESS sectors and are validated with ground-based photometric follow-up, precise radial-velocity measurements, and high-resolution imaging. We used the software package juliet to jointly model the photometric and radial-velocity datasets, with Gaussian processes applied to correct for systematics. The three planets discovered in the TOI-663 system are low-mass mini-Neptunes with radii significantly larger than those of rocky analogs, implying that volatiles, such as water, must predominate. In addition to this internal structure analysis, we also performed a dynamical analysis that confirmed the stability of the system. The three exoplanets in the TOI-663 system, similarly to other sub-Neptunes orbiting M dwarfs, have been found to have lower densities than planets of similar sizes orbiting stars of different spectral types.
Context.
The current architecture of a given multi-planetary system is a key fingerprint of its past formation and dynamical evolution history. Long-term follow-up observations are key to complete ...their picture.
Aims.
In this paper, we focus on the confirmation and characterization of the components of the TOI-969 planetary system, where TESS detected a Neptune-size planet candidate in a very close-in orbit around a late K-dwarf star.
Methods.
We use a set of precise radial velocity observations from HARPS, PFS, and CORALIE instruments covering more than two years in combination with the TESS photometric light curve and other ground-based follow-up observations to confirm and characterize the components of this planetary system.
Results.
We find that TOI-969 b is a transiting close-in (
P
b
~ 1.82 days) mini-Neptune planet (
m
b
= 9.1
−1.0
+1.1
M
⊕
,
R
b
= 2.765
−0.097
+0.088
R
⊕
), placing it on the lower boundary of the hot-Neptune desert (
T
eq,b
= 941 ± 31 K). The analysis of its internal structure shows that TOI-969 b is a volatile-rich planet, suggesting it underwent an inward migration. The radial velocity model also favors the presence of a second massive body in the system, TOI-969 c, with a long period of
P
c
= 1700
−280
+290
days, a minimum mass of
m
c
sin
i
c
= 11.3
−0.9
+1.1
M
Jup
, and a highly eccentric orbit of
e
c
= 0.628
−0.036
+0.043
.
Conclusions.
The TOI-969 planetary system is one of the few around K-dwarfs known to have this extended configuration going from a very close-in planet to a wide-separation gaseous giant. TOI-969 b has a transmission spectroscopy metric of 93 and orbits a moderately bright (
G
= 11.3 mag) star, making it an excellent target for atmospheric studies. The architecture of this planetary system can also provide valuable information about migration and formation of planetary systems.
The Transiting Exoplanet Survey Satellite (TESS) provides a continuous suite of new planet candidates that need confirmation and precise mass determination from ground-based observatories. This is ...the case for the G-type star TOI-1710, which is known to host a transiting sub-Saturn planet ( M p = 28.3 ± 4.7 M ⊕ ) in a long-period orbit ( P = 24.28 days). Here we combine archival SOPHIE and new and archival HARPS-N radial velocity data with newly available TESS data to refine the planetary parameters of the system and derive a new mass measurement for the transiting planet, taking into account the impact of the stellar activity on the mass measurement. We report for TOI-1710b a radius of R p = 5.15 ± 0.12 R ⊕ , a mass of M p = 18.4 ± 4.5 M ⊕ , and a mean bulk density of ρ p = 0.73 ± 0.18 g cm −3 , which are consistent at 1.2 σ , 1.5 σ , and 0.7 σ , respectively, with previous measurements. Although there is not a significant difference in the final mass measurement, we needed to add a Gaussian process component to successfully fit the radial velocity dataset. This work illustrates that adding more measurements does not necessarily imply a better mass determination in terms of precision, even though they contribute to increasing our full understanding of the system. Furthermore, TOI-1710b joins an intriguing class of planets with radii in the range 4–8 R ⊕ that have no counterparts in the Solar System. A large gaseous envelope and a bright host star make TOI-1710b a very suitable candidate for follow-up atmospheric characterization.
We present high-resolution X-ray spectroscopy of two recent g-ray burst (GRB) afterglows observed with the Low Energy Transmission Grating Spectrometer on Chandra. The afterglows to GRBs 030328 and ...041006 are detected beginning 15.33 and 16.8 hr after each burst, respectively, and are observed to fade in time during each 690 ks observation. We fit for the continuum emission in each full data set and for the data sliced into half and quarter time sections. For both afterglows, the continuum emission is well described by an absorbed power-law model, and the model parameters describing the absorption and spectral slope do not appear to evolve in time. We perform a careful search for deviations from the model continua for the full and time-sliced data and find no evidence for significant ( 3 s) narrow emission/absorption lines or edges. The lack of detections implies that line emission--if it is a general feature in GRB X-ray afterglows--occurs early (t 6 0.3 days in the source frame) and/or is short-lived (dt 10 ks). We also comment on synchrotron fireball models for the X-ray and optical data.
Aims
.
We report the discovery and validation of two TESS exoplanets orbiting faint M dwarfs: TOI-4479b and TOI-2081b.
Methods
.
We jointly analyzed space (TESS mission) and ground-based (MuSCAT2, ...MuSCAT3 and SINISTRO instruments) light curves using our multicolor photometry transit analysis pipeline. This allowed us to compute contamination limits for both candidates and validate them as planet-sized companions.
Results
.
We found TOI-4479b to be a sub-Neptune-sized planet (
R
p
= 2.82
−0.63
+0.65
R
⊕
) and TOI-2081b to be a super-Earth-sized planet (
R
p
= 2.04
−0.54
+0.50
R
⊕
). Furthermore, we obtained that TOI-4479b, with a short orbital period of 1.15890
−0.00001
+0.00002
days, lies within the Neptune desert and is in fact the largest nearly ultra-short period planet around an M dwarf known to date.
Conclusions
.
These results make TOI-4479b rare among the currently known exoplanet population of M dwarf stars and an especially interesting target for spectroscopic follow-up and future studies of planet formation and evolution.
Context.
Tidal orbital decay is suspected to occur for hot Jupiters in particular, with the only observationally confirmed case of this being WASP-12b. By examining this effect, information on the ...properties of the host star can be obtained using the so-called stellar modified tidal quality factor
Q
*
′
, which describes the efficiency with which the kinetic energy of the planet is dissipated within the star. This can provide information about the interior of the star.
Aims.
In this study, we aim to improve constraints on the tidal decay of the KELT-9, KELT-16, and WASP-4 systems in order to find evidence for or against the presence of tidal orbital decay. With this, we want to constrain the
Q
*
′
value for each star. In addition, we aim to test the existence of the transit timing variations (TTVs) in the HD 97658 system, which previously favoured a quadratic trend with increasing orbital period.
Methods.
Making use of newly acquired photometric observations from CHEOPS (CHaracterising ExOplanet Satellite) and TESS (Transiting Exoplanet Survey Satellite), combined with archival transit and occultation data, we use Markov chain Monte Carlo (MCMC) algorithms to fit three models to the data, namely a constant-period model, an orbital-decay model, and an apsidal-precession model.
Results.
We find that the KELT-9 system is best described by an apsidal-precession model for now, with an orbital decay trend at over 2
σ
being a possible solution as well. A Keplerian orbit model with a constant orbital period provides the best fit to the transit timings of KELT-16 b because of the scatter and scale of their error bars. The WASP-4 system is best represented by an orbital decay model at a 5
σ
significance, although apsidal precession cannot be ruled out with the present data. For HD 97658 b, using recently acquired transit observations, we find no conclusive evidence for a previously suspected strong quadratic trend in the data.
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