4,039 research outputs found
Carbon monoxide and water vapor in the atmosphere of the non-transiting exoplanet HD 179949 b
(Abridged) In recent years, ground-based high-resolution spectroscopy has
become a powerful tool for investigating exoplanet atmospheres. It allows the
robust identification of molecular species, and it can be applied to both
transiting and non-transiting planets. Radial-velocity measurements of the star
HD 179949 indicate the presence of a giant planet companion in a close-in
orbit. Here we present the analysis of spectra of the system at 2.3 micron,
obtained at a resolution of R~100,000, during three nights of observations with
CRIRES at the VLT. We targeted the system while the exoplanet was near superior
conjunction, aiming to detect the planet's thermal spectrum and the radial
component of its orbital velocity. We detect molecular absorption from carbon
monoxide and water vapor with a combined S/N of 6.3, at a projected planet
orbital velocity of K_P = (142.8 +- 3.4) km/s, which translates into a planet
mass of M_P = (0.98 +- 0.04) Jupiter masses, and an orbital inclination of i =
(67.7 +- 4.3) degrees, using the known stellar radial velocity and stellar
mass. The detection of absorption features rather than emission means that,
despite being highly irradiated, HD 179949 b does not have an atmospheric
temperature inversion in the probed range of pressures and temperatures. Since
the host star is active (R_HK > -4.9), this is in line with the hypothesis that
stellar activity damps the onset of thermal inversion layers owing to UV flux
photo-dissociating high-altitude, optical absorbers. Finally, our analysis
favors an oxygen-rich atmosphere for HD 179949 b, although a carbon-rich planet
cannot be statistically ruled out based on these data alone.Comment: 10 pages, 9 figures. Accepted for publication in Astronomy and
Astrophysic
The GROUSE project III: Ks-band observations of the thermal emission from WASP-33b
In recent years, day-side emission from about a dozen hot Jupiters has been
detected through ground-based secondary eclipse observations in the
near-infrared. These near-infrared observations are vital for determining the
energy budgets of hot Jupiters, since they probe the planet's spectral energy
distribution near its peak. The aim of this work is to measure the Ks-band
secondary eclipse depth of WASP-33b, the first planet discovered to transit an
A-type star. This planet receives the highest level of irradiation of all
transiting planets discovered to date. Furthermore, its host-star shows
pulsations and is classified as a low-amplitude delta-Scuti. As part of our
GROUnd-based Secondary Eclipse (GROUSE) project we have obtained observations
of two separate secondary eclipses of WASP-33b in the Ks-band using the LIRIS
instrument on the William Herschel Telescope (WHT). The telescope was
significantly defocused to avoid saturation of the detector for this bright
star (K~7.5). To increase the stability and the cadence of the observations,
they were performed in staring mode. We collected a total of 5100 and 6900
frames for the first and the second night respectively, both with an average
cadence of 3.3 seconds. On the second night the eclipse is detected at the
12-sigma level, with a measured eclipse depth of 0.244+0.027-0.020 %. This
eclipse depth corresponds to a brightness temperature of 3270+115-160 K. The
measured brightness temperature on the second night is consistent with the
expected equilibrium temperature for a planet with a very low albedo and a
rapid re-radiation of the absorbed stellar light. For the other night the short
out-of-eclipse baseline prevents good corrections for the stellar pulsations
and systematic effects, which makes this dataset unreliable for eclipse depth
measurements. This demonstrates the need of getting a sufficient out-of-eclipse
baseline.Comment: 12 pages, 10 figures. Accepted for publication in Astronomy and
Astrophysic
Searching for solar-like oscillations in the delta Scuti star rho Puppis
Despite the shallow convective envelopes of delta Scuti pulsators, solar-like
oscillations are theoretically predicted to be excited in those stars as well.
To search for such stochastic oscillations we organised a spectroscopic
multi-site campaign for the bright, metal-rich delta Sct star rho Puppis. We
obtained a total of 2763 high-resolution spectra using four telescopes. We
discuss the reduction and analysis with the iodine cell technique, developed
for searching for low-amplitude radial velocity variations, in the presence of
high-amplitude variability. Furthermore, we have determined the angular
diameter of rho Puppis to be 1.68 \pm 0.03 mas, translating into a radius of
3.52 \pm 0.07Rsun. Using this value, the frequency of maximum power of possible
solar-like oscillations, is expected at ~43 \pm 2 c/d (498 \pm 23 muHz). The
dominant delta Scuti-type pulsation mode of rho Puppis is known to be the
radial fundamental mode which allows us to determine the mean density of the
star, and therefore an expected large frequency separation of 2.73 c/d (31.6
muHz). We conclude that 1) the radial velocity amplitudes of the delta Scuti
pulsations are different for different spectral lines; 2) we can exclude
solar-like oscillations to be present in rho Puppis with an amplitude per
radial mode larger than 0.5 m/s.Comment: 14 pages, 12 figure, accepted for MNRA
Exoplanet atmospheres with GIANO. I. Water in the transmission spectrum of HD 189733b
High-resolution spectroscopy (R 20,000) at near-infrared wavelengths
can be used to investigate the composition, structure, and circulation patterns
of exoplanet atmospheres. However, up to now it has been the exclusive dominion
of the biggest telescope facilities on the ground, due to the large amount of
photons necessary to measure a signal in high-dispersion spectra. Here we show
that spectrographs with a novel design - in particular a large spectral range -
can open exoplanet characterisation to smaller telescope facilities too. We aim
to demonstrate the concept on a series of spectra of the exoplanet HD 189733 b
taken at the Telescopio Nazionale Galileo with the near-infrared spectrograph
GIANO during two transits of the planet. In contrast to absorption in the
Earth's atmosphere (telluric absorption), the planet transmission spectrum
shifts in radial velocity during transit due to the changing orbital motion of
the planet. This allows us to remove the telluric spectrum while preserving the
signal of the exoplanet. The latter is then extracted by cross-correlating the
residual spectra with template models of the planet atmosphere computed through
line-by-line radiative transfer calculations, and containing molecular
absorption lines from water and methane. By combining the signal of many
thousands of planet molecular lines, we confirm the presence of water vapour in
the atmosphere of HD 189733 b at the 5.5- level. This signal was
measured only in the first of the two observing nights. By injecting and
retrieving artificial signals, we show that the non-detection on the second
night is likely due to an inferior quality of the data. The measured strength
of the planet transmission spectrum is fully consistent with past CRIRES
observations at the VLT, excluding a strong variability in the depth of
molecular absorption lines.Comment: 10 pages, 8 figures. Accepted for publication in Astronomy &
Astrophysics. v2 includes language editin
Detection of water absorption in the day side atmosphere of HD 189733 b using ground-based high-resolution spectroscopy at 3.2 microns
We report a 4.8 sigma detection of water absorption features in the day side
spectrum of the hot Jupiter HD 189733 b. We used high-resolution (R~100,000)
spectra taken at 3.2 microns with CRIRES on the VLT to trace the
radial-velocity shift of the water features in the planet's day side atmosphere
during 5 h of its 2.2 d orbit as it approached secondary eclipse. Despite
considerable telluric contamination in this wavelength regime, we detect the
signal within our uncertainties at the expected combination of systemic
velocity (Vsys=-3 +5-6 km/s) and planet orbital velocity (Kp=154 +14-10 km/s),
and determine a H2O line contrast ratio of (1.3+/-0.2)x10^-3 with respect to
the stellar continuum. We find no evidence of significant absorption or
emission from other carbon-bearing molecules, such as methane, although we do
note a marginal increase in the significance of our detection to 5.1 sigma with
the inclusion of carbon dioxide in our template spectrum. This result
demonstrates that ground-based, high-resolution spectroscopy is suited to
finding not just simple molecules like CO, but also to more complex molecules
like H2O even in highly telluric contaminated regions of the Earth's
transmission spectrum. It is a powerful tool that can be used for conducting an
immediate census of the carbon- and oxygen-bearing molecules in the atmospheres
of giant planets, and will potentially allow the formation and migration
history of these planets to be constrained by the measurement of their
atmospheric C/O ratios.Comment: 5 pages, 4 figures, accepted for publication in MNRAS Letter
Ancillary service provision by demand side management : a real-time power hardware-in-the-loop co-simulation demonstration
The role of demand side management in providing ancillary services to the network is an active topic of research. However, their implementation is limited due to lack of practical demonstrations and tests that can rigorously quantify their ability to support the grid’s integrity. In this paper, provision of time critical frequency control ancillary service is demonstrated by means of integrating PowerMatcher, a well discussed demand side management mechanism in literature, with real-time power hardware. The co-simulation platform enables testing of demand side management techniques to provide ancillary services
Optical Interferometry of early-type stars with PAVO@CHARA. I. Fundamental stellar properties
We present interferometric observations of 7 main-sequence and 3 giant stars
with spectral types from B2 to F6 using the PAVO beam combiner at the CHARA
array. We have directly determined the angular diameters for these objects with
an average precision of 2.3%. We have also computed bolometric fluxes using
available photometry in the visible and infrared wavelengths, as well as
space-based ultraviolet spectroscopy. Combined with precise \textit{Hipparcos}
parallaxes, we have derived a set of fundamental stellar properties including
linear radius, luminosity and effective temperature. Fitting the latter to
computed isochrone models, we have inferred masses and ages of the stars. The
effective temperatures obtained are in good agreement (at a 3% level) with
nearly-independent temperature estimations from spectroscopy. They validate
recent sixth-order polynomial (B-V)- empirical relations
\citep{Boyajian2012a}, but suggest that a more conservative third-order
solution \citep{vanBelle2009} could adequately describe the
(V-K)- relation for main-sequence stars of spectral type A0 and
later. Finally, we have compared mass values obtained combining surface gravity
with inferred stellar radius (\textit{gravity mass}) and as a result of the
comparison of computed luminosity and temperature values with stellar
evolutionary models (\textit{isochrone mass}). The strong discrepancy between
isochrone and gravity mass obtained for one of the observed stars,
\,Lyr, suggests that determination of the stellar atmosphere parameters
should be revised.Comment: 13 pages, 9 figures, accepted for publication in MNRA
Evidence for the disintegration of KIC 12557548 b
Context. The Kepler object KIC 12557548 b is peculiar. It exhibits
transit-like features every 15.7 hours that vary in depth between 0.2% and
1.2%. Rappaport et al. (2012) explain the observations in terms of a
disintegrating, rocky planet that has a trailing cloud of dust created and
constantly replenished by thermal surface erosion. The variability of the
transit depth is then a consequence of changes in the cloud optical depth.
Aims. We aim to validate the disintegrating-planet scenario by modeling the
detailed shape of the observed light curve, and thereby constrain the cloud
particle properties to better understand the nature of this intriguing object.
Methods. We analysed the six publicly-available quarters of raw Kepler data,
phase-folded the light curve and fitted it to a model for the trailing dust
cloud. Constraints on the particle properties were investigated with a
light-scattering code. Results. The light curve exhibits clear signatures of
light scattering and absorption by dust, including a brightening in flux just
before ingress correlated with the transit depth and explained by forward
scattering, and an asymmetry in the transit light curve shape, which is easily
reproduced by an exponentially decaying distribution of optically thin dust,
with a typical grain size of 0.1 micron. Conclusions. Our quantitative analysis
supports the hypothesis that the transit signal of KIC 12557548 b is due to a
variable cloud of dust, most likely originating from a disintegrating object.Comment: 5 pages, 4 figures. Accepted for publication in Astronomy and
Astrophysic
- …