TY  - JOUR
A1  - Schaffenroth, Veronika
A1  - Casewell, Sarah L.
A1  - Schneider, D.
A1  - Kilkenny, David
A1  - Geier, Stephan
A1  - Heber, Ulrich
A1  - Irrgang, Andreas
A1  - Przybilla, Norbert
A1  - Marsh, Thomas R.
A1  - Littlefair, Stuart P.
A1  - Dhillon, Vik S.
T1  - A quantitative in-depth analysis of the prototype sdB plus BD system SDSS J08205+0008 revisited in the Gaia era
JF  - Monthly notices of the Royal Astronomical Society
N2  - Subdwarf B stars are core-helium-burning stars located on the extreme horizontal branch (EHB). Extensive mass loss on the red giant branch is necessary to form them. It has been proposed that substellar companions could lead to the required mass loss when they are engulfed in the envelope of the red giant star. J08205+0008 was the first example of a hot subdwarf star with a close, substellar companion candidate to be found. Here, we perform an in-depth re-analysis of this important system with much higher quality data allowing additional analysis methods. From the higher resolution spectra obtained with ESO-VLT/XSHOOTER, we derive the chemical abundances of the hot subdwarf as well as its rotational velocity. Using the Gaia parallax and a fit to the spectral energy distribution in the secondary eclipse, tight constraints to the radius of the hot subdwarf are derived. From a long-term photometric campaign, we detected a significant period decrease of -3.2(8) x 10(-12) dd(-1). This can be explained by the non-synchronized hot subdwarf star being spun up by tidal interactions forcing it to become synchronized. From the rate of period decrease we could derive the synchronization time-scale to be 4 Myr, much smaller than the lifetime on EHB. By combining all different methods, we could constrain the hot subdwarf to a mass of 0.39-0.50 M-circle dot and a radius of R-sdB = 0.194 +/- 0.008 R-circle dot, and the companion to 0.061-0.071 M-circle dot with a radius of R-comp = 0.092 +/- 0.005 R-circle dot, below the hydrogen-burning limit. We therefore confirm that the companion is most likely a massive brown dwarf.
KW  - stars: abundances
KW  - stars: atmospheres
KW  - stars: fundamental parameters
KW  - stars: horizontal branch
KW  - stars: low-mass
KW  - subdwarfs
Y1  - 2020
U6  - https://doi.org/10.1093/mnras/staa3661
SN  - 0035-8711
SN  - 1365-2966
VL  - 501
IS  - 3
SP  - 3847
EP  - 3870
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - GEN
A1  - Finch, Nicolle L.
A1  - Braker, I. P.
A1  - Reindl, Nicole
A1  - Barstow, Martin A.
A1  - Casewell, Sarah L.
A1  - Burleigh, M.
A1  - Kupfer, Thomas
A1  - Kilkenny, D.
A1  - Geier, Stephan Alfred
A1  - Schaffenroth, Veronika
A1  - Bertolami Miller, Marcelo Miguel
A1  - Taubenberger, Stefan
A1  - Freudenthal, Joseph
T1  - Spectral Analysis of Binary Pre-white Dwarf Systems
T2  - Radiative signatures from the cosmos
N2  - Short period double degenerate white dwarf (WD) binaries with periods of less than similar to 1 day are considered to be one of the likely progenitors of type Ia supernovae. These binaries have undergone a period of common envelope evolution. If the core ignites helium before the envelope is ejected, then a hot subdwarf remains prior to contracting into a WD. Here we present a comparison of two very rare systems that contain two hot subdwarfs in short period orbits. We provide a quantitative spectroscopic analysis of the systems using synthetic spectra from state-of-the-art non-LTE models to constrain the atmospheric parameters of the stars. We also use these models to determine the radial velocities, and thus calculate dynamical masses for the stars in each system.
Y1  - 2019
SN  - 978-1-58381-925-8
SN  - 1050-3390
VL  - 519
SP  - 231
EP  - 238
PB  - Astronomical soc pacific
CY  - San Fransisco
ER  - 
TY  - JOUR
A1  - Reindl, Nicole
A1  - Finch, Nicolle L.
A1  - Schaffenroth, Veronika
A1  - Barstow, Martin A.
A1  - Casewell, Sarah L.
A1  - Geier, Stephan Alfred
A1  - Bertolami Miller, Marcelo Miguel
A1  - Taubenberger, Stefan
T1  - Revealing the true nature of Hen 2-428
JF  - Galaxies
N2  - The nucleus of Hen 2-428 is a short orbital period (4.2 h) spectroscopic binary, whose status as potential supernovae type Ia progenitor has raised some controversy in the literature. We present preliminary results of a thorough analysis of this interesting system, which combines quantitative non-local thermodynamic (non-LTE) equilibrium spectral modelling, radial velocity analysis, multi-band light curve fitting, and state-of-the art stellar evolutionary calculations. Importantly, we find that the dynamical system mass that is derived by using all available He II lines does not exceed the Chandrasekhar mass limit. Furthermore, the individual masses of the two central stars are too small to lead to an SN Ia in case of a dynamical explosion during the merger process.
KW  - binaries: spectroscopic
KW  - stars: atmospheres
KW  - stars: abundances
KW  - supernovae
Y1  - 2018
U6  - https://doi.org/10.3390/galaxies6030088
SN  - 2075-4434
VL  - 6
IS  - 3
ER  - 
TY  - JOUR
A1  - Eigmüller, Philipp
A1  - Chaushev, Alexander
A1  - Gillen, Edward
A1  - Smith, Alexis
A1  - Nielsen, Louise D.
A1  - Turner, Oliver
A1  - Csizmadia, Szilard
A1  - Smalley, Barry
A1  - Bayliss, Daniel
A1  - Belardi, Claudia
A1  - Bouchy, Francois
A1  - Burleigh, Matthew R.
A1  - Cabrera, Juan
A1  - Casewell, Sarah L.
A1  - Chazelas, Bruno
A1  - Cooke, Benjamin F.
A1  - Erikson, Anders
A1  - Gansicke, Boris T.
A1  - Guenther, Maximilian N.
A1  - Goad, Michael R.
A1  - Grange, Andrew
A1  - Jackman, James A. G.
A1  - Jenkins, James S.
A1  - McCormac, James
A1  - Moyano, Maximiliano
A1  - Pollacco, Don
A1  - Poppenhäger, Katja
A1  - Queloz, Didier
A1  - Raynard, Liam
A1  - Rauer, Heike
A1  - Udry, Stephane
A1  - Walker, Simon. R.
A1  - Watson, Christopher A.
A1  - West, Richard G.
A1  - Wheatley, Peter J.
T1  - NGTS-5b
BT  - a highly inflated planet offering insights into the sub-Jovian desert
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. Planetary population analysis gives us insight into formation and evolution processes. For short-period planets, the sub-Jovian desert has been discussed in recent years with regard to the planet population in the mass/period and radius/period parameter space without taking stellar parameters into account. The Next Generation Transit Survey (NGTS) is optimised for detecting planets in this regime, which allows for further analysis of the sub-Jovian desert. Aims. With high-precision photometric surveys (e.g. with NGTS and TESS), which aim to detect short period planets especially around M/K-type host stars, stellar parameters need to be accounted for when empirical data are compared to model predictions. Presenting a newly discovered planet at the boundary of the sub-Jovian desert, we analyse its bulk properties and use it to show the properties of exoplanets that border the sub-Jovian desert. Methods. Using NGTS light curve and spectroscopic follow-up observations, we confirm the planetary nature of planet NGTS-5b and determine its mass. Using exoplanet archives, we set the planet in context with other discoveries. Results. NGTS-5b is a short-period planet with an orbital period of 3.3569866 +/- 0.0000026 days. With a mass of 0.229 +/- 0.037 M-Jup and a radius of 1.136 +/- 0.023 R-Jup, it is highly inflated. Its mass places it at the upper boundary of the sub-Jovian desert. Because the host is a K2 dwarf, we need to account for the stellar parameters when NGTS-5b is analysed with regard to planet populations. Conclusions. With red-sensitive surveys (e.g. with NGTS and TESS), we expect many more planets around late-type stars to be detected. An empirical analysis of the sub-Jovian desert should therefore take stellar parameters into account.
KW  - planets and satellites: detection
KW  - planets and satellites: gaseous planets
Y1  - 2019
U6  - https://doi.org/10.1051/0004-6361/201935206
SN  - 1432-0746
VL  - 625
PB  - EDP Sciences
CY  - Les Ulis
ER  -