2,426 research outputs found
Comparative Planetary Atmospheres: Models of TrES-1 and HD209458b
We present new self-consistent atmosphere models for transiting planets
TrES-1 and HD209458b. The planets were recently observed with the Spitzer Space
Telescope in bands centered on 4.5 and 8.0 m, for TrES-1, and 24 m,
for HD209458b. We find that standard solar metallicity models fit the
observations for HD209458b. For TrES-1, which has an T_eff ~300 K cooler, we
find that models with a metallicity 3-5 times enhanced over solar abundances
can match the 1 error bar at 4.5 m and 2 at 8.0m.
Models with solar abundances that included energy deposition into the
stratosphere give fluxes that fall within the 2 error bars in both
bands. The best-fit models for both planets assume that reradiation of absorbed
stellar flux occurs over the entire planet. For all models of both planets we
predict planet/star flux ratios in other Spitzer bandpasses.Comment: Accepted to the Astrophysical Journal Letters, May 17, 200
Is there evidence for change to collagen within parchment samples after exposure to an X-ray dose during high contrast X-ray microtomography? a multi technique investigation
OA MOnitor ExerciseOA MOnitor ExerciseOA MOnitor ExerciseOA MOnitor ExerciseThe potential use of high contrast X-ray microtomography (XMT) for the reading of fragile historic documents without the need to physically unravel them is a new analytical imaging development in the field of conservation however, it is important to first assess if there is any evidence of change in the parchment structure during scanning by XMT. Modern and historic parchment samples were exposed to X-rays using the high contrast XMT equipment. Attenuated Total Reflection Fourier Transform Infra-red Spectroscopy (ATR-FTIR), SDS-polyacrylamide gel electrophoresis (SDS-PAGE), Near-infrared Spectroscopy (NIR) and X-ray diffraction (XRD) were utilised to investigate whether there is any evidence for change to collagen within parchment samples after exposure to XMT. Results show that the inherent differences in the parchment structure due to the material source, production and storage appear to produce larger differences than that due to the exposure to XMT. This indicates that XMT may be a suitable technique for data recovery from parchment samples that cannot be unrolled.This research was supported by funding received from the Engineering, Physical Sciences Research Council EP/G007845/1 and EP/G010110/1
A Spitzer/IRAC Search for Substellar Companions of the Debris Disk Star epsilon Eridani
We have used the InfraRed Array Camera (IRAC) onboard the Spitzer Space
telescope to search for low mass companions of the nearby debris disk star
epsilon Eridani. The star was observed in two epochs 39 days apart, with
different focal plane rotation to allow the subtraction of the instrumental
Point Spread Function, achieving a maximum sensitivity of 0.01 MJy/sr at 3.6
and 4.5 um, and 0.05 MJy/sr at 5.8 and 8.0 um. This sensitivity is not
sufficient to directly detect scattered or thermal radiation from the epsilon
Eridani debris disk. It is however sufficient to allow the detection of Jovian
planets with mass as low as 1 MJ in the IRAC 4.5 um band. In this band, we
detected over 460 sources within the 5.70 arcmin field of view of our images.
To test if any of these sources could be a low mass companion to epsilon
Eridani, we have compared their colors and magnitudes with models and
photometry of low mass objects. Of the sources detected in at least two IRAC
bands, none fall into the range of mid-IR color and luminosity expected for
cool, 1 Gyr substellar and planetary mass companions of epsilon Eridani, as
determined by both models and observations of field M, L and T dwarf. We
identify three new sources which have detections at 4.5 um only, the lower
limit placed on their [3.6]-[4.5] color consistent with models of planetary
mass objects. Their nature cannot be established with the currently available
data and a new observation at a later epoch will be needed to measure their
proper motion, in order to determine if they are physically associated to
epsilon Eridani.Comment: 36 pages, to be published on The Astrophysical Journal, vol. 647,
August 200
Spectroscopic Detection of Carbon Monoxide in Two Late-type T Dwarfs
M band spectra of two late-type T dwarfs, 2MASS J09373487+2931409, and Gliese
570D, confirm evidence from photometry that photospheric CO is present at
abundance levels far in excess of those predicted from chemical equilibrium.
These new and unambiguous detections of CO, together with an earlier
spectroscopic detection of CO in Gliese 229B and existing M band photometry of
a large selection of T dwarfs, suggest that vertical mixing in the photosphere
drives the CO abundance out of chemical equilibrium and is a common, and likely
universal feature of mid-to-late type T dwarfs. The M band spectra allow
determinations of the time scale of vertical mixing in the atmosphere of each
object, the first such measurements of this important parameter in late T
dwarfs. A detailed analysis of the spectral energy distribution of 2MASS
J09373487+2931409 results in the following values for metallicity, temperature,
surface gravity, and luminosity: [M/H]~-0.3, T_eff=925-975K, log g=5.20-5.47,
log L/L_sun=-5.308 +/- 0.027. The age is 3-10 Gyr and the mass is in the range
45-69 M_Jup.Comment: 36 pages incl. 12 figures and 3 tables, accepted by Ap
First Space-Based Microlens Parallax Measurement: Spitzer Observations of OGLE-2005-SMC-001
We combine Spitzer and ground-based observations to measure the microlens
parallax of OGLE-2005-SMC-001, the first such space-based determination since
S. Refsdal proposed the idea in 1966. The parallax measurement yields a
projected velocity \tilde v ~ 230 km/s, the typical value expected for halo
lenses, but an order of magnitude smaller than would be expected for lenses
lying in the Small Magellanic Cloud (SMC) itself. The lens is a weak (i.e.,
non-caustic-crossing) binary, which complicates the analysis considerably but
ultimately contributes additional constraints. Using a test proposed by Assef
et al. (2006), which makes use only of kinematic information about different
populations but does not make any assumptions about their respective mass
functions, we find that the likelihood ratio is L_halo/L_SMC = 20. Hence, halo
lenses are strongly favored but SMC lenses are not definitively ruled out.
Similar Spitzer observations of additional lenses toward the Magellanic Clouds
would clarify the nature of the lens population. The Space Interferometry
Mission could make even more constraining measurements.Comment: ApJ, in press. Text and figures are updated to match the journal
versio
Properties of the T8.5 Dwarf Wolf 940 B
We present 7.5-14.2um low-resolution spectroscopy, obtained with the Spitzer
Infrared Spectrograph, of the T8.5 dwarf Wolf 940 B, which is a companion to an
M4 dwarf with a projected separation of 400 AU. We combine these data with
previously published near-infrared spectroscopy and mid-infrared photometry, to
produce the spectral energy distribution for the very low-temperature T dwarf.
We use atmospheric models to derive the bolometric correction and obtain a
luminosity of log L/Lsun = -6.01 +/- 0.05. Evolutionary models are used with
the luminosity to constrain the values of effective temperature (T_eff) and
surface gravity, and hence mass and age for the T dwarf. We further restrict
the allowed range of T_eff and gravity using age constraints implied by the M
dwarf primary, and refine the physical properties of the T dwarf by comparison
of the observed and modelled spectroscopy and photometry. This comparison
indicates that Wolf 940 B has a metallicity within 0.2 dex of solar, as more
extreme values give poor fits to the data - lower metallicity produces a poor
fit at lambda > 2um while higher metallicity produces a poor fit at lambda <
2um. This is consistent with the independently derived value of [m/H] = +0.24
+/- 0.09 for the primary star, using the Johnson & Apps (2008) M_K:V-K
relationship. We find that the T dwarf atmosphere is undergoing vigorous
mixing, with an eddy diffusion coefficient K_zz of 10^4 to 10^6 cm^2 s^-1. We
derive an effective temperature of 585 K to 625 K, and surface gravity log g =
4.83 to 5.22 (cm s^-2), for an age range of 3 Gyr to 10 Gyr, as implied by the
kinematic and H alpha properties of the M dwarf primary. The lower gravity
corresponds to the lower temperature and younger age for the system, and the
higher value to the higher temperature and older age. The mass of the T dwarf
is 24 M_Jupiter to 45 M_Jupiter for the younger to older age limit.Comment: 24 pages which include 5 Figures and 3 Tables. Accepted for
publication in the Astrophysical Journal July 2 201
- …