In order to investigate the near wing of the Lyman-
α
line, accurate line profile calculations and molecular data are both required due to the existence of a close line satellite responsible for its ...asymmetrical shape. Lyman-
α
lines observed with the Cosmic Origin Spectograph on the
Hubble
Space Telescope show this peculiarity in the spectra of DBA and DA white dwarf stars. A similar asymmetrical shape in the blue wing can be predicted in the Balmer-
α
line of H perturbed by He and H atoms. In continuation with a very recent work on the Lyman-
α
line, where the
n
= 2 potential energies and transition dipole moments from the ground state were determined, we present new accurate H-He potential energies and electronic transition dipole moments involving the molecular states correlated with H(
n
= 3)+He and their transition dipole moments with the states correlated with H(
n
= 2)+He. Those new data and existing molecular data for H(
n
= 2,3)-H are used to provide a theoretical investigation of the collisional effects in the blue wing of the Balmer-
α
line of H perturbed by He and H atoms. We note the consequences for the Balmer-
α
line shape in the physical conditions found in the cool atmosphere of DZA white dwarfs where helium densities may be as high as 10
21
cm
−3
. This study is undertaken with a unified theory of spectral line broadening valid at very high helium densities.
In this paper we emphasize the non-Lorentzian behavior of the Balmer series in helium-dominated DBA white dwarf stars for which the decades-old problem exists for the determination of the hydrogen ...abundance. In a very recent work, we have shown that quasi-molecular line satellites due to H-He and H-H collisions are responsible for the asymmetrical shape of the Lyman-
α
lines observed with the Cosmic Origin Spectrograph and that a similar asymmetry exists for the Balmer-
α
line profiles. In continuation with very recent work, where the
n
= 2, 3 potential energies and transition dipole moments from the ground state were determined, here, we present accurate H-He potential energies and electronic transition dipole moments concerning the molecular states correlated with H(
n
= 4)+He and their transition dipole moments with the states correlated with H(
n
= 2)+He. Those new data are used to provide a theoretical investigation of the collisional effects in the blue wing of the Balmer-
β
line of H perturbed by He. Because of the general trend characterizing the repulsive Σ states of the potential energies involved in the Balmer series, the amplitude in the core of the line is decreasing very fast with the order of the series when the helium density gets as large as 10
21
cm
−3
. This study is undertaken by applying a unified theory of spectral line broadening that is valid at very high helium densities found in DZA white dwarf stars. The treatment includes collision-induced line satellites due to asymptotically forbidden transitions, and it explains the asymmetry observed in their spectra.
Observations of cooler and cooler brown dwarfs show that the contribution from broadening at many bars pressure is becoming important. The opacity in the red optical to near-IR region under these ...conditions is dominated by the extremely pressure-broadened wings of the alkali resonance lines, in particular, the K I resonance doublet at 0.77 μm. Collisions with H2 are preponderant in brown dwarf atmospheres at an effective temperature of about 1000 K; the H2 perturber densities reach several 1019 even in Jupiter-mass planets and exceed 1020 for super-Jupiters and older Y dwarfs. As a consequence, it appears that when the far wing absorption due to alkali atoms in a dense H2 atmosphere is significant, accurate pressure broadened profiles that are valid at high densities of H2 should be incorporated into spectral models.
Context. The effects of collision broadening by He are central to understanding the opacity of cool stellar atmospheres. Aims. DZ white dwarfs show metal lines which are, in many cases, believed to ...come from some rocky material, a remnant of a former exoplanetary system. The analysis of the Mg+ resonance lines is a valuable method to determine the chemical abundances in these systems. Methods. Unified profiles of the strongest of the UV lines of Mg+ have been calculated in the semi-classical approach using very recent ab initio potential energies. Results. We present the first theoretical line profile calculations of the resonance lines of Mg+ that have been perturbed by helium in physical conditions of atmospheres in helium-rich white dwarfs with metal traces.
The analysis of the far wings of resonance lines of alkali elements in brown dwarf spectra requires their accurate determination. A unified theory of collisional line profiles has been applied for ...the evaluation of absorption profiles of alkalis perturbed by helium and molecular hydrogen. The study of the dependence on temperature of the far wings of Li–He and Li–H2 collisional profiles is reported.
Context. Line shapes of the magnesium resonance lines in white dwarf spectra are determined by the properties of magnesium atoms and the structure of the white dwarf atmosphere. Through their ...blanketing effect, these lines have a dominant influence on the model structure and thus on the determination from the spectra of other physical parameters that describe the stellar atmosphere and elemental abundances. Aims. In continuation of previous work on Mg+He lines in the UV, we present theoretical profiles of the resonance line of neutral Mg perturbed by He at the extreme density conditions found in the cool largely transparent atmosphere of DZ white dwarfs. Methods. We accurately determined the broadening of Mg by He in a unified theory of collisional line profiles using ab initio calculations of MgHe potential energies and transition matrix elements among the singlet electronic states that are involved for the observable spectral lines. Results. We computed the shapes and line parameters of the Mg lines and studied their dependence on helium densities and temperatures. We present results over the full range of temperatures from 4000 to 12 000 K needed for input to stellar spectra models. Atmosphere models were constructed for a range of effective temperatures and surface gravities typical for cool DZ white dwarfs. We present synthetic spectra tracing the behavior of the Mg resonance line profiles under the low temperatures and high gas pressures prevalent in these atmospheres. Conclusions. The determination of accurate opacity data of magnesium resonance lines together with an improved atmosphere model code lead to a good fit of cool DZ white dwarf stars. The broadening of spectral lines by helium needs to be understood to accurately determine the H/He and Mg/He abundance ratio in DZ white dwarf atmospheres. We emphasize that no free potential parameters or ad hoc adjustments were used to calculate the line profiles.
The Transiting Exoplanet Survey Satellite TESS has begun a new age of exoplanet discoveries around bright host stars. We present the discovery of HD 1397b (TOI-120.01), a giant planet in an 11.54-day ...eccentric orbit around a bright (V = 7.9) G-type subgiant. We estimate both host star and planetary parameters consistently using EXOFASTv2 based on TESS time-series photometry of transits and radial velocity measurements with CORALIE and MINERVA-Australis. We also present high angular resolution imaging with NaCo to rule out any nearby eclipsing binaries. We find that HD 1397b is a Jovian planet, with a mass of 0.415 ± 0.020 MJ and a radius of 1.026 ± 0.026 RJ. Characterising giant planets in short-period eccentric orbits, such as HD 1397b, is important for understanding and testing theories for the formation and migration of giant planets as well as planet-star interactions.
Spectral observations below Lyman-
α
are now obtained with the Cosmic Origin Spectrograph (COS) on the
Hubble
Space Telescope. It is therefore necessary to provide an accurate treatment of the blue ...wing of the Lyman-
α
line that enables correct calculations of radiative transport in DA and DBA white dwarf stars. On the theoretical front, we very recently developed very accurate H-He potential energies for the hydrogen 1s, 2s, and 2p states. Nevertheless, an uncertainty remained about the asymptotic correlation of the Σ states and the electronic dipole transition moments. A similar difficulty occurred in our first calculations for the resonance broadening of hydrogen perturbed by collisions with neutral H atoms. The aim of this paper is twofold. First, we clarify the question of the asymptotic correlation of the Σ states, and we show that relativistic contributions, even very tiny, may need to be accounted for a correct long-range and asymptotic description of the states because of the specific 2s 2p Coulomb degeneracy in hydrogen. This effect of relativistic corrections, inducing small splitting of the 2s and 2p states of H, is shown to be important for the Σ-Σ transition dipole moments in H-He and is also discussed in H-H. Second, we use existent (H-H) and newly determined (H-He) accurate potentials and properties to provide a theoretical investigation of the collisional effects on the blue wing of the Lyman-
α
line of H perturbed by He and H. We study the relative contributions in the blue wing of the H and He atoms according to their relative densities. We finally achieve a comparison with recent COS observations and propose an assignment for a feature centered at 1190 Å.
Observations of cooler and cooler brown dwarfs show that the contribution from broadening at many bars pressure is becoming important. The opacity in the red optical to near-IR region under these ...conditions is dominated by the extremely pressure-broadened wings of the alkali resonance lines, in particular, the K I resonance doublet at 0.77 µm. Collisions with H 2 are preponderant in brown dwarf atmospheres at an effective temperature of about 1000 K; the H 2 perturber densities reach several 10 19 even in Jupiter-mass planets and exceed 10 20 for super-Jupiters and older Y dwarfs. As a consequence, it appears that when the far wing absorption due to alkali atoms in a dense H 2 atmosphere is significant, accurate pressure broadened profiles that are valid at high densities of H 2 should be incorporated into spectral models.
Three short-period Jupiters from TESS Nielsen, L. D.; Brahm, R.; Bouchy, F. ...
Astronomy and astrophysics (Berlin),
07/2020, Letnik:
639
Journal Article, Web Resource
Recenzirano
Odprti dostop
We report the confirmation and mass determination of three hot Jupiters discovered by the Transiting Exoplanet Survey Satellite (TESS) mission: HIP 65Ab (TOI-129, TIC-201248411) is an ...ultra-short-period Jupiter orbiting a bright (
V
= 11.1 mag) K4-dwarf every 0.98 days. It is a massive 3.213 ± 0.078
M
J
planet in a grazing transit configuration with an impact parameter of
b
= 1.17
−0.08
+0.10
. As a result the radius is poorly constrained, 2.03
−0.49
+0.61
R
J
. The planet’s distance to its host star is less than twice the separation at which it would be destroyed by Roche lobe overflow. It is expected to spiral into HIP 65A on a timescale ranging from 80 Myr to a few gigayears, assuming a reduced tidal dissipation quality factor of
Q
s
′
= 10
7
− 10
9
. We performed a full phase-curve analysis of the TESS data and detected both illumination- and ellipsoidal variations as well as Doppler boosting. HIP 65A is part of a binary stellar system, with HIP 65B separated by 269 AU (3.95 arcsec on sky). TOI-157b (TIC 140691463) is a typical hot Jupiter with a mass of 1.18 ± 0.13
M
J
and a radius of 1.29 ± 0.02
R
J
. It has a period of 2.08 days, which corresponds to a separation of just 0.03 AU. This makes TOI-157 an interesting system, as the host star is an evolved G9 sub-giant star (
V
= 12.7). TOI-169b (TIC 183120439) is a bloated Jupiter orbiting a
V
= 12.4 G-type star. It has a mass of 0.79 ±0.06
M
J
and a radius of 1.09
−0.05
+0.08
R
J
. Despite having the longest orbital period (
P
= 2.26 days) of the three planets, TOI-169b receives the most irradiation and is situated on the edge of the Neptune desert. All three host stars are metal rich with Fe / H ranging from 0.18 to0.24.
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