2,265 research outputs found
Excitonic Dynamical Franz-Keldysh Effect
The Dynamical Franz-Keldysh Effect is exposed by exploring near-bandgap
absorption in the presence of intense THz electric fields. It bridges the gap
between the DC Franz- Keldysh effect and multi-photon absorption and competes
with the THz AC Stark Effect in shifting the energy of the excitonic resonance.
A theoretical model which includes the strong THz field non-perturbatively via
a non-equilibrium Green Functions technique is able to describe the Dynamical
Franz-Keldysh Effect in the presence of excitonic absorption.Comment: 4 pages in revtex with 5 figures included using epsf. Submitted to
Physical Review Letter
Characterizing Transiting Extrasolar Planets with Narrow-Band Photometry and GTC/OSIRIS
We report the first extrasolar planet observations from the 10.4-m Gran
Telescopio Canarias (GTC), currently the world's largest, fully steerable,
single-aperture optical telescope. We used the OSIRIS tunable filter imager on
the GTC to acquire high-precision, narrow-band photometry of the transits of
the giant exoplanets, TrES-2b and TrES-3b. We obtained near-simultaneous
observations in two near-infrared (NIR) wavebands (790.2 and 794.4 +/- 2.0 nm)
specifically chosen to avoid water vapor absorption and skyglow so as to
minimize the atmospheric effects that often limit the precision of ground-based
photometry. Our results demonstrate a very-high photometric precision with
minimal atmospheric contamination despite relatively poor atmospheric
conditions and some technical problems with the telescope. We find the
photometric precision for the TrES-2 observations to be 0.343 and 0.412 mmag
for the 790.2 and 794.4 nm light curves, and the precision of the TrES-3
observations was found to be 0.470 and 0.424 mmag for the 790.2 and 794.4 nm
light curves. We also discuss how future follow-up observations of transiting
planets with this novel technique can contribute to the characterization of
Neptune- and super-Earth-size planets to be discovered by space-based missions
like CoRoT and Kepler, as well as measure atmospheric properties of giant
planets, such as the strength of atmospheric absorption features.Comment: 9 pages, including 3 figures and 2 tables; accepted for publication
in MNRA
Escaping Particle fluxes in the atmospheres of close-in exoplanets: I. model of hydrogen
A multi-fluid model for an atomic hydrogen-proton mixture in the upper
atmosphere of extrosolar planet is presented when the continuity and momentum
equations of each component have been already solved with an energy equation.
The particle number density, the temperature distribution and the structure of
velocity can be found by means of the model. We chose two special objects, HD
209458b and HD 189733b, as discussion samples and the conclusion is that their
mass loss rates predicted by the model are in accordance with those of
observation. The most important physical process in coupling each component is
charge exchange which tightly couples atomic hydrogen with protons. Most of the
hydrogen escaping from hot Jupiters is protons, especially in young star-planet
system. We found that the single-fluid model can describe the escape of
particles when the mass loss rate is higher than a few times g/s while
below g/s the multi-fluid model is more suitable for it due to the
decoupling of particles. We found that the predicted mass loss rates of HD
189733b with the assumption of energy-limit are a factor of 10 larger than that
calculated by our models due to the high ionization degree. For the ionized
wind which is almost compose of protons, the assumption of energy-limit is no
longer effective. We fitted the mass loss rates of the ionized wind as a
function of by calculating the variation of the mass loss rates with
UV fluxes.Comment: 35 pages, 6 figures, submitted to Ap
Independent confirmation and refined parameters of the hot Jupiter XO-5b
We present HATNet observations of XO-5b, confirming its planetary nature
based on evidence beyond that described in the announcement of Burke et al.
(2008), namely, the lack of significant correlation between spectral bisector
variations and orbital phase. In addition, using extensive spectroscopic
measurements spanning multiple seasons, we investigate the relatively large
scatter in the spectral line bisectors. We also examine possible blended
stellar configurations (hierarchical triples, chance alignments) that can mimic
the planet signals, and we are able to show that none are consistent with the
sum of all the data. The analysis of the S activity index shows no significant
stellar activity. Our results for the planet parameters are consistent with
values in Burke et al. (2008), and we refine both the stellar and planetary
parameters using our data. XO-5b orbits a slightly evolved, late G type star
with mass M_s = 0.88 +/- 0.03, radius R_s = 1.08 +/- 0.04, and metallicity
close to solar. The planetary mass and radius are M_p = 1.059 +/- 0.028 M_Jup
and R_p = 1.109 +/- 0.050 R_Jup, respectively, corresponding to a mean density
of 0.96 -0.11 +0.14 g/cm^3. The ephemeris for the orbit is P = 4.187757 +/-
0.000011, E= 2454552.67168 +/- 0.00029 (BJD) with transit duration of 0.1307
+/- 0.0013 d. By measuring four individual transit centers, we found no signs
for transit timing variations. The planet XO-5b is notable for its anomalously
high Safronov number, and has a high surface gravity when compared to other
transiting exoplanets with similar period.Comment: Accepted for publication in ApJ, 8 pages in emulateapj styl
HAT-P-15b: A 10.9-day Extrasolar Planet Transiting a Solar-type Star
We report the discovery of HAT-P-15b, a transiting extrasolar planet in the
`period valley', a relatively sparsely-populated period regime of the known
extrasolar planets. The host star, GSC 2883-01687, is a G5 dwarf with V=12.16.
It has a mass of 1.01+/-0.04 M(Sun), radius of 1.08+/-0.04 R(Sun), effective
temperature 5568+/-90 K, and metallicity [Fe/H] = +0.22+/-0.08. The planetary
companion orbits the star with a period 10.863502+/-0.000027 days, transit
epoch Tc = 2454638.56019+/-0.00048 (BJD), and transit duration 0.2285+/-0.0015
days. It has a mass of 1.946+/-0.066 M(Jup), and radius of 1.072+/-0.043 R(Jup)
yielding a mean density of 1.96+/-0.22 g/cm3. At an age of 6.8+/-2.1 Gyr, the
planet is H/He-dominated and theoretical models require about 2% (10 M(Earth))
worth of heavy elements to reproduce its measured radius. With an estimated
equilibrium temperature of 820 K during transit, and 1000 K at occultation,
HAT-P-15b is a potential candidate to study moderately cool planetary
atmospheres by transmission and occultation spectroscopy.Comment: 12 pages with 10 figures and 6 tables in emulateapj format. Submitted
to The Astrophysical Journa
The climate of HD 189733b from fourteen transits and eclipses measured by Spitzer
We present observations of seven transits and seven eclipses of the
transiting planet system HD 189733 taken with Spitzer IRAC at 8 microns. We use
a new correction for the detector ramp variation with a double-exponential
function. Our main findings are: (1) an upper limit on the variability of the
day-side planet flux of 2.7% (68% confidence); (2) the most precise set of
transit times measured for a transiting planet, with an average accuracy of 3
seconds; (3) a lack of transit-timing variations, excluding the presence of
second planets in this system above 20% of the mass of Mars in low-order
mean-motion resonance at 95% confidence; (4) a confirmation of the planet's
phase variation, finding the night side is 64% as bright as the day side, as
well as an upper limit on the night-side variability of 17% (68% confidence);
(5) a better correction for stellar variability at 8 micron causing the phase
function to peak 3.5 hrs before secondary eclipse, confirming that the
advection and radiation timescales are comparable at the 8 micron photosphere;
(6) variation in the depth of transit, which possibly implies variations in the
surface brightness of the portion of the star occulted by the planet, posing a
fundamental limit on non-simultaneous multi-wavelength transit absorption
measurements of planet atmospheres; (7) a measurement of the infrared
limb-darkening of the star, in agreement with stellar atmosphere models; (8) an
offset in the times of secondary eclipse of 69 sec, which is mostly accounted
for by a 31 sec light travel time delay and 33 sec delay due to the shift of
ingress and egress by the planet hot spot; this confirms that the phase
variation is due to an offset hot spot on the planet; (9) a retraction of the
claimed eccentricity of this system due to the offset of secondary eclipse; and
(10) high precision measurements of the parameters of this system.Comment: 18 pages, 19 figures, accepted for publication in the Astrophysical
Journa
Detection of transit timing variations in excess of one hour in the Kepler multi-planet candidate system KOI 806 with the GTC
We report the detection of transit timing variations (TTVs) well in excess of
one hour in the Kepler multi-planet candidate system KOI 806. This system
exhibits transits consistent with three separate planets -- a Super-Earth, a
Jupiter, and a Saturn -- lying very nearly in a 1:2:5 resonance, respectively.
We used the Kepler public data archive and observations with the Gran
Telescopio de Canarias to compile the necessary photometry. For the largest
candidate planet (KOI 806.02) in this system, we detected a large transit
timing variation of -103.56.9 minutes against previously published
ephemeris. We did not obtain a strong detection of a transit color signature
consistent with a planet-sized object; however, we did not detect a color
difference in transit depth, either. The large TTV is consistent with
theoretical predictions that exoplanets in resonance can produce large transit
timing variations, particularly if the orbits are eccentric. The presence of
large TTVs among the bodies in this systems indicates that KOI806 is very
likely to be a planetary system. This is supported by the lack of a strong
color dependence in the transit depth, which would suggest a blended eclipsing
binary.Comment: 9 pages, 4 figures, accepted into A&A Letter
HAT-P-11b: A Super-Neptune Planet Transiting a Bright K Star in the Kepler Field
We report on the discovery of HAT-P-11b, the smallest radius transiting
extrasolar planet (TEP) discovered from the ground, and the first hot Neptune
discovered to date by transit searches. HAT-P-11b orbits the bright (V=9.587)
and metal rich ([Fe=H] = +0.31 +/- 0.05) K4 dwarf star GSC 03561-02092 with P =
4.8878162 +/- 0.0000071 days and produces a transit signal with depth of 4.2
mmag. We present a global analysis of the available photometric and
radial-velocity data that result in stellar and planetary parameters, with
simultaneous treatment of systematic variations. The planet, like its near-twin
GJ 436b, is somewhat larger than Neptune (17Mearth, 3.8Rearth) both in mass Mp
= 0.081 +/- 0.009 MJ (25.8 +/- 2.9 Mearth) and radius Rp = 0.422 +/- 0.014 RJ
(4.73 +/- 0.16 Rearth). HAT-P-11b orbits in an eccentric orbit with e = 0.198
+/- 0.046 and omega = 355.2 +/- 17.3, causing a reflex motion of its parent
star with amplitude 11.6 +/- 1.2 m/s, a challenging detection due to the high
level of chromospheric activity of the parent star. Our ephemeris for the
transit events is Tc = 2454605.89132 +/- 0.00032 (BJD), with duration 0.0957
+/- 0.0012 d, and secondary eclipse epoch of 2454608.96 +/- 0.15 d (BJD). The
basic stellar parameters of the host star are M* = 0.809+0.020-0.027 Msun, R* =
0.752 +/- 0.021 Rsun and Teff = 4780 +/- 50 K. Importantly, HAT-P-11 will lie
on one of the detectors of the forthcoming Kepler mission. We discuss an
interesting constraint on the eccentricity of the system by the transit light
curve and stellar parameters. We also present a blend analysis, that for the
first time treats the case of a blended transiting hot Jupiter mimicing a
transiting hot Neptune, and proves that HAT-P-11b is not such a blend.Comment: Accepted for publication in ApJ, 24 pages, 14 figures, 6 tables. All
RV data presented in this versio
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