403 research outputs found
Gas Absorption Detected from the Edge-on Debris Disk Surrounding HD32297
Near-infrared and optical imaging of HD32297 indicate that it has an edge-on
debris disk, similar to beta Pic. I present high resolution optical spectra of
the NaI doublet toward HD32297 and stars in close angular proximity. A
circumstellar absorption component is clearly observed toward HD32297 at the
stellar radial velocity, which is not observed toward any of its neighbors,
including the nearest only 0.9 arcmin away. An interstellar component is
detected in all stars >90 pc, including HD32297, likely due to the interstellar
material at the boundary of the Local Bubble. Radial velocity measurements of
the nearest neighbors, BD+07 777s and BD+07 778, indicate that they are
unlikely to be physically associated with HD32297. The measured circumstellar
column density around HD32997, log N(NaI) ~ 11.4, is the strongest NaI
absorption measured toward any nearby main sequence debris disk, even the
prototypical edge-on debris disk, beta Pic. Assuming that the morphology and
abundances of the gas component around HD32297 are similar to beta Pic, I
estimate an upper limit to the gas mass in the circumstellar disk surrounding
HD32297 of ~0.3 M_Earth.Comment: 13 pages, 2 figures; Accepted for publication in ApJ Letter
Exoplanet HD 209458b : Evaporation strengthened
Following re-analysis of Hubble Space Telescope observations of primary
transits of the extrasolar planet HD209458b at Lyman-alpha, Ben-Jaffel (2007,
BJ007) claims that no sign of evaporation is observed. Here we show that, in
fact, this new analysis is consistent with the one of Vidal-Madjar et al.
(2003, VM003) and supports the detection of evaporation. The apparent
disagreement is mainly due to the disparate wavelength ranges that are used to
derive the transit absorption depth. VM003 derives a (15+/-4)% absorption depth
during transit over the core of the stellar Lyman-alpha line (from -130 km/s to
+100 km/s), and this result agrees with the (8.9+/-2.1)% absorption depth
reported by BJ007 from a slightly expanded dataset but over a larger wavelength
range (+/-200 km/s). These measurements agree also with the (5+/-2)% absorption
reported by Vidal-Madjar et al. (2004) over the whole Lyman-alpha line from
independent, lower-resolution data. We show that stellar Lyman-alpha
variability is unlikely to significantly affect those detections. The HI atoms
must necessarily have velocities above the escape velocities and/or be outside
the Roche lobe, given the lobe shape and orientation. Absorption by HI in
HD209458b's atmosphere has thus been detected with different datasets, and now
with independent analyses. All these results strengthen the concept of
evaporating hot-Jupiters, as well as the modelization of this phenomenon.Comment: To be published in ApJ
The deuterium-to-oxygen ratio in the interstellar medium
Because the ionization balances for HI, OI, and DI are locked together by
charge exchange, D/O is an important tracer for the value of the D/H ratio and
for potential spatial variations in the ratio. As the DI and OI column
densities are of similar orders of magnitude for a given sight line,
comparisons of the two values will generally be less subject to systematic
errors than comparisons of DI and HI, which differ by about five orders of
magnitude. Moreover, D/O is additionally sensitive to astration, because as
stars destroy deuterium, they should produce oxygen. We report here the results
of a survey of D/O in the interstellar medium performed with FUSE. We also
compare these results with those for D/N. Together with a few results from
previous missions, the sample totals 24 lines of sight. The distances range
from a few pc to ~2000 pc and log N(DI) from ~13 to ~16 (cm-2). The D/O ratio
is constant in the local interstellar medium out to distances of ~150 pc and
N(DI) ~ 1x10^15 cm-2, i.e. within the Local Bubble. In this region of the
interstellar space, we find D/O = (3.84+/-0.16)x10^-2 (1 sigma in the mean).
The homogeneity of the local D/O measurements shows that the spatial variations
in the local D/H and O/H must be extremely small, if any. A comparison of the
Local Bubble mean value with the few D/O measurements available for low
metallicity quasar sight lines shows that the D/O ratio decreases with cosmic
evolution, as expected. Beyond the Local Bubble we detected significant spatial
variations in the value of D/O. This likely implies a variation in D/H, as O/H
is known to not vary significantly over the distances covered in this study.
Our dataset suggests a present-epoch deuterium abundance below 1x10^-5, i.e.
lower than the value usually assumed, around 1.5x10^-5.Comment: 17 pages, 9 figures, 4 tables, accepted for publication in the
Astrophysical Journa
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