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 (Rp = 2.82−0.63+0.65 R⊕) and TOI-2081b to be a super-Earth-sized planet (Rp = 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.
We examine the X-ray spectra and variability of the sample of X-ray sources with L sub(X) approximately 10 super(31)-10 super(33) ergs s super(-1) identified within the inner 9' of the Galaxy by Muno ...et al. Very few of the sources exhibit intraday or intermonth variations. We find that the spectra of the point sources near the Galactic center are very hard between 2-8 keV, even after accounting for absorption. When modeled as power laws, the median photon index is Gamma = 0.7, while when modeled as thermal plasma we can only obtain lower limits to the temperature of kT > 8 keV. The combined spectra of the point sources is similarly hard, with a photon index of Gamma = 0.8. Strong line emission is observed from low-ionization, He-like, and H-like Fe, both in the average spectra and in the brightest individual sources. The line ratios of the highly ionized Fe in the average spectra are consistent with emission from a plasma in thermal equilibrium. This line emission is observed whether average spectra are examined as a function of the count rate from the source or as a function of the hardness ratios of individual sources. This suggests that the hardness of the spectra may in fact be to due local absorption that partially covers the X-ray-emitting regions in the Galactic center systems. We suggest that most of these sources are intermediate polars, which (1) often exhibit hard spectra with prominent Fe lines, (2) rarely exhibit either flares on short timescales or changes in their mean X-ray flux on long timescales, and (3) are the most numerous hard X-ray sources with comparable luminosities in the Galaxy.
Abstract
We report the discovery of four transiting giant planets around K dwarfs. The planets HATS-47b, HATS-48Ab, HATS-49b, and HATS-72b have masses of
,
,
, and
, respectively, and radii of
,
,
, ...and
, respectively. The planets orbit close to their host stars with orbital periods of
days,
days,
days, and
days, respectively. The hosts are main-sequence K dwarfs with masses of
,
,
, and
, and with
V
-band magnitudes of
,
,
and
. The super-Neptune HATS-72b (a.k.a. WASP-191b and TOI 294.01) was independently identified as a transiting planet candidate by the HATSouth, WASP, and
TESS
surveys, and we present a combined analysis of all of the data gathered by each of these projects (and their follow-up programs). An exceptionally precise mass is measured for HATS-72b thanks to high-precision radial velocity (RV) measurements obtained with VLT/ESPRESSO, FEROS, HARPS, and
Magellan
/PFS. We also incorporate
TESS
observations of the warm Saturn–hosting systems HATS-47 (a.k.a. TOI 1073.01), HATS-48A, and HATS-49. HATS-47 was independently identified as a candidate by the
TESS
team, while the other two systems were not previously identified from the
TESS
data. The RV orbital variations are measured for these systems using
Magellan
/PFS. HATS-48A has a resolved
neighbor in
Gaia
DR2, which is a common-proper-motion binary star companion to HATS-48A with a mass of 0.22
and a current projected physical separation of ∼1400 au.
The GAPS programme at TNG Naponiello, L.; Mancini, L.; Damasso, M. ...
Astronomy and astrophysics (Berlin),
11/2022, Letnik:
667
Journal Article
Recenzirano
Odprti dostop
Context
.
Neptunes represent one of the main types of exoplanets and have chemical-physical characteristics halfway between rocky and gas giant planets. Therefore, their characterization is important ...for understanding and constraining both the formation mechanisms and the evolution patterns of planets.
Aims
.
We investigate the exoplanet candidate TOI-1422 b, which was discovered by the TESS space telescope around the high proper-motion G2 V star TOI-1422 (V = 10.6 mag), 155 pc away, with the primary goal of confirming its planetary nature and characterising its properties.
Methods
.
We monitored TOI-1422 with the HARPS-N spectrograph for 1.5 yr to precisely quantify its radial velocity (RV) variation. We analyse these RV measurements jointly with TESS photometry and check for blended companions through high-spatial resolution images using the AstraLux instrument.
Results
.
We estimate that the parent star has a radius of
R
⋆
= 1.019
−0.013
+0.014
R
⊙
, and a mass of
M
⋆
= 1.019
−0.013
+0.014
M
⊙
. Our analysis confirms the planetary nature of TOI-1422 b and also suggests the presence of a Neptune-mass planet on a more distant orbit, the candidate TOI-1422 c, which is not detected in TESS light curves. The inner planet, TOI-1422 b, orbits on a period of
P
b
= 12.9972 ± 0.0006 days and has an equilibrium temperature of
T
eq,b
= 867 ± 17 K. With a radius of
R
b
= 3.96
−0.11
+0.13
R
⊕
, a mass of
M
b
= 9.0
−2.0
+2.3
M
⊕
and, consequently, a density of
ρ
b
= 0.795
−0.235
+0.290
g cm
−3
, it can be considered a warm Neptune-sized planet. Compared to other exoplanets of a similar mass range, TOI-1422 b is among the most inflated, and we expect this planet to have an extensive gaseous envelope that surrounds a core with a mass fraction around 10% – 25% of the total mass of the planet. The outer non-transiting planet candidate, TOI-1422 c, has an orbital period of
P
c
= 29.29
−0.20
+0.21
days, a minimum mass,
M
c
sin
i,
of 11.1
−2.3
+2.6
M
⊕
, an equilibrium temperature of
T
eq,c
= 661 ± 13 K and, therefore, if confirmed, could be considered as another warm Neptune.
During the fabrication of niobium superconducting radio frequency (SRF) particle accelerator cavities procedures are used that chemically or mechanically remove the passivating surface film of ...niobium pentoxide (Nb2O5). Removal of this film will expose the underlying niobium metal and allow it to react with the processing environment. If these reactions produce hydrogen at sufficient concentrations and rates, then hydrogen will be absorbed and diffuse into the metal. High hydrogen activities could result in supersaturation and the nucleation of hydride phases. If the metal repassivates at the conclusion of the processing step and the passive film blocks hydrogen egress, then the absorbed hydrogen or hydrides could be retained and alter the performance of the metal during subsequent processing steps or in-service. This report examines the feasibility of this hypothesis by first identifying the postulated events, conditions, and reactions and then determining if each is consistent with accepted scientific principles, literature, and data. Established precedent for similar events in other systems was found in the scientific literature and thermodynamic analysis found that the postulated reactions were not only energetically favorable, but produced large driving forces. The hydrogen activity or fugacity required for the reactions to be at equilibrium was determined to indicate the propensity for hydrogen evolution, absorption, and hydride nucleation. The influence of processing conditions and kinetics on the proximity of hydrogen surface coverage to these theoretical values is discussed. This examination found that the hypothesis of hydrogen absorption during SRF processing is consistent with published scientific literature and thermodynamic principles.
ABSTRACT
Transiting exoplanets orbiting young nearby stars are ideal laboratories for testing theories of planet formation and evolution. However, to date only a handful of stars with age <1 Gyr have ...been found to host transiting exoplanets. Here we present the discovery and validation of a sub-Neptune around HD 18599 , a young (300 Myr), nearby (d = 40 pc) K star. We validate the transiting planet candidate as a bona fide planet using data from the TESS , Spitzer , and Gaia missions, ground-based photometry from IRSF , LCO , PEST , and NGTS , speckle imaging from Gemini, and spectroscopy from CHIRON , NRES , FEROS , and Minerva-Australis . The planet has an orbital period of 4.13 d , and a radius of 2.7 R⊕ . The RV data yields a 3-σ mass upper limit of 30.5 M⊕ which is explained by either a massive companion or the large observed jitter typical for a young star. The brightness of the host star (V∼9 mag) makes it conducive to detailed characterization via Doppler mass measurement which will provide a rare view into the interior structure of young planets.
Context. Transiting sub-Neptune-type planets, with radii approximately between 2 and 4R⊕, are of particular interest as their study allows us to gain insight into the formation and evolution of a ...class of planets that are not found in our Solar System. Aims. We exploit the extreme radial velocity (RV) precision of the ultra-stable echelle spectrograph ESPRESSO on the VLT to unveil the physical properties of the transiting sub-Neptune TOI-130 b, uncovered by the TESS mission orbiting the nearby, bright, late F-typestar HD 5278 (TOI-130) with a period of Pb=14.3 days. Methods. We used 43 ESPRESSO high-resolution spectra and broad-band photometry information to derive accurate stellar atmospheric and physical parameters of HD 5278. We exploited the TESS light curve and spectroscopic diagnostics to gauge the impact of stellar activity on the ESPRESSO RVs. We performed separate as well as joint analyses of the TESS photometry and the ESPRESSORVs using fully Bayesian frameworks to determine the system parameters. Results. Based on the ESPRESSO spectra, the updated stellar parameters of HD 5278 are Teff=6203±64K, logg=4.50±0.11dex, Fe/H =−0.12±0.04dex,M?=1.126+0.036−0.035M, and R?=1.194+0.017−0.016R. We determine HD 5278 b’s mass and radius to be Mb=7.8+1.5−1.4M⊕ and Rb=2.45±0.05R⊕. The derived mean density, %b=2.9+0.6−0.5g cm−3, is consistent with the bulk composition of a sub-Neptune with a substantial (∼30%) water mass fraction and with a gas envelope comprising ∼17% of the measured radius. Given the host brightness and irradiation levels, HD 5278 b is one of the best targets orbiting G-F primaries for follow-up atmospheric characterization measurements with HST and JWST. We discover a second, non-transiting companion in the system, with a period of Pc=40.87+0.18−0.17days and a minimum mass of Mcsinic=18.4+1.8−1.9M⊕. We study emerging trends in parameters space (e.g., mass, radius, stellar insolation, and mean density) of the growing population of transiting sub-Neptunes, and provide statistical evidence for a low occurrence of close-in,10−15M⊕companions around G-F primaries withTeff&5500K.
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 (Mcore = 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 X ( O ) core = 0 . 16 − 0.05 + 0.13 $ X(\mathrm{O})_{\mathrm{core}}=0.16_{-0.05}^{+0.13} $ ) 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 12C(α, γ)16O nuclear reaction rate.
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