162 research outputs found
Asteroseismology with SuperWASP
The highly successful SuperWASP planetary transit finding programme has
surveyed a large fraction of both the northern and southern skies. There now
exists in the its archive over 420 billion photometric measurements for more
than 31 million stars. SuperWASP provides good quality photometry with a
precision exceeding 1% per observation in the approximate magnitude range 9 < V
< 12. The archive enables long-baseline, high-cadence studies of stellar
variability to be undertaken. An overview of the SuperWASP project is
presented, along with results which demonstrate the survey's asteroseismic
capabilities.Comment: 4 pages, 4 figures. To appear in proceedings of IAU Symposium 301,
Precision Asteroseismology, August 2013, Wroc{\l}aw, Polan
Different convection models in ATLAS
Convection is an important phenomenon in the atmospheres of A-type and cooler
stars. A description of convection in ATLAS models is presented, together with
details of how it is specified in model calculations. The effects of changing
the treatment of convection on model structures and how this affects observable
quantities are discussed. The role of microturbulence is examined, and its link
to velocity fields within the atmosphere. Far from being free parameters,
mixing-length and microturbulence should be constrained in model calculations.Comment: 7 pages, 6 figures. To appear in the proceedings of the Workshop
"ATLAS 12 and related codes", Trieste, July 11-15, 200
Observations of convection in A-type stars
Convection and turbulence in stellar atmospheres have a significant effect on
the emergent flux from A-type stars. The recent theoretical advancements in
convection modelling have proved a challenge to the observers to obtain
measurements with sufficient precision and accuracy to allow discrimination
between the various predictions.
A discussion of the current observational techniques used to evaluate the
various convection theories is presented. These include filter photometry,
spectrophotometry, hydrogen lines, and metal lines. The results from these
techniques are given, along with the successes and limitations.Comment: 8 pages, 4 figures, Invited Lecture at IAU Symposium 224 "The A Star
Puzzle", 7-13 July 2004, Poprad, Slovaki
Stellar Fluxes as Probes of Convection in Stellar Atmospheres
Convection and turbulence in stellar atmospheres have a significant effect on
the emergent flux from late-type stars. The theoretical advancements in
convection modelling over recent years have proved challenging for the
observers to obtain measurements with sufficient precision and accuracy to
allow discrimination between the various predictions.
An overview of the current observational techniques used to evaluate various
convection theories is presented, including photometry, spectrophotometry, and
spectroscopy. The results from these techniques are discussed, along with their
successes and limitations.
The prospects for improved observations of stellar fluxes are also given.Comment: 3 pages, 1 figure; to appear in Convection in Astrophysics, Proc.
IAUS 239, F.Kupka, I.W. Roxburgh, K.L. Chan ed
Teff and log g Determinations
A discussion on the determination of effective temperature (Teff) and surface
gravity (log g) is presented. The observational requirements for
model-independent fundamental parameters are summarized, including an
assessment of the accuracy of these values for the Sun and Vega. The use of
various model-dependent techniques for determining Teff and log g are outlined,
including photometry, flux fitting, and spectral line ratios. A combination of
several of these techniques allows for the assessment of the quality of our
parameter determinations. While some techniques can give precise parameter
determinations, the overall accuracy of the values is significantly less and
sometimes difficult to quantify.Comment: 10 pages, 5 figures. To appear in the proceedings of the Workshop
"ATLAS 12 and related codes", Trieste, July 11-15, 200
NGTS-10b: the shortest period hot Jupiter yet discovered
We report the discovery of a new ultrashort period (USP) transiting hot Jupiter from the Next Generation Transit Survey (NGTS). NGTS-10b has a mass and radius of 2.162+0.092-0.107?MJ and 1.205+0.117-0.083?RJ and orbits its host star with a period of 0.7668944 ± 0.0000003?d, making it the shortest period hot Jupiter yet discovered. The host is a 10.4 ± 2.5?Gyr old K5V star (Teff = 4400 ± 100?K) of Solar metallicity ([Fe/H] = -0.02 ± 0.12?dex) showing moderate signs of stellar activity. NGTS-10b joins a short list of USP Jupiters that are prime candidates for the study of star–planet tidal interactions. NGTS-10b orbits its host at just 1.46 ± 0.18 Roche radii, and we calculate a median remaining inspiral time of 38?Myr and a potentially measurable orbital period decay of 7 s over the coming decade, assuming a stellar tidal quality factor Q's =2 × 107
NGTS-5b: a highly inflated planet offering insights into the sub-Jovian desert
Context: Planetary population analysis gives us insight into formation and evolution processes. For short-period planets, the subJovian 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 MJup and a radius of 1.136 +- 0.023 RJup, 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
Teff and log g Determinations
A discussion on the determination of effective temperature (Teff) and surface gravity (log g) is presented. The observational requirements for model-independent fundamental parameters are summarized, including an assessment of the accuracy of these values for the Sun and Vega. The use of various model-dependent techniques for determining Teff and log g are outlined, including photometry, flux fitting, and spectral line ratios. A combination of several of these techniques allows for the assessment of the quality of our parameter determinations. While some techniques can give precise parameter determinations, the overall accuracy of the values is significantly less and sometimes difficult to quantify
Observations of convection in A-type stars
Convection and turbulence in stellar atmospheres have a significant effect on the emergent flux from A-type stars. The recent theoretical advancements in convection modelling have proved a challenge to the observers to obtain measurements with sufficient precision and accuracy to allow discrimination between the various predictions. A discussion of the current observational techniques used to evaluate the various convection theories is presented. These include filter photometry, spectrophotometry, hydrogen lines, and metal lines. The results from these techniques are given, along with the successes and limitations
- …