1,427 research outputs found
High-Resolution Near Infrared Spectroscopy of HD 100546: II. Analysis of variable rovibrational CO emission lines
We present observations of rovibrational CO in HD 100546 from four epochs
spanning January 2003 through December 2010. We show that the equivalent widths
of the CO lines vary during this time period with the v=1-0 CO lines
brightening more than the UV fluoresced lines from the higher vibrational
states. While the spectroastrometric signal of the hot band lines remains
constant during this period, the spectroastrometric signal of the v=1--0 lines
varies substantially. At all epochs, the spectroastrometric signals of the UV
fluoresced lines are consistent with the signal one would expect from gas in an
axisymmetric disk. In 2003, the spectroastrometric signal of the v=1-0 P26 line
was symmetric and consistent with emission from an axisymmetric disk. However,
in 2006, there was no spatial offset of the signal detected on the red side of
the profile, and in 2010, the spectroastrometric offset was yet more strongly
reduced toward zero velocity. A model is presented that can explain the
evolution of the equivalent width of the v=1-0 P26 line and its
spectroastrometric signal by adding to the system a compact source of CO
emission that orbits the star near the inner edge of the disk. We hypothesize
that such emission may arise from a circumplanetary disk orbiting a gas giant
planet near the inner edge of the circumstellar disk. We discuss how this idea
can be tested observationally and be distinguished from an alternative
interpretation of random fluctuations in the disk emission.Comment: 18 pages, 10 figure
High-Resolution Near Infrared Spectroscopy of HD 100546: I. Analysis of Asymmetric Ro-Vibrational OH Emission Lines
We present observations of ro-vibrational OH and CO emission from the Herbig
Be star HD 100546. The emission from both molecules arises from the inner
region of the disk extending from approximately 13 AU from the central star.
The velocity profiles of the OH lines are narrower than the velocity profile of
the [O I] 6300 Angstrom line indicating that the OH in the disk is not
cospatial with the O I. This suggests that the inner optically thin region of
the disk is largely devoid of molecular gas. Unlike the ro-vibrational CO
emission lines, the OH lines are highly asymmetric. We show that the average CO
and average OH line profiles can be fit with a model of a disk comprised of an
eccentric inner wall and a circular outer disk. In this model, the vast
majority of the OH flux (75%) originates from the inner wall, while the vast
majority of the CO flux (65%) originates on the surface of the disk at radii
greater than 13 AU. Eccentric inner disks are predicted by hydrodynamic
simulations of circumstellar disks containing an embedded giant planet. We
discuss the implications of such a disk geometry in light of models of planet
disk tidal interactions and propose alternate explanations for the origin of
the asymmetry
Accretion variability of Herbig Ae/Be stars observed by X-Shooter. HD 31648 and HD 163296
This work presents X-Shooter/VLT spectra of the prototypical, isolated Herbig
Ae stars HD 31648 (MWC 480) and HD 163296 over five epochs separated by
timescales ranging from days to months. Each spectrum spans over a wide
wavelength range covering from 310 to 2475 nm. We have monitored the continuum
excess in the Balmer region of the spectra and the luminosity of twelve
ultraviolet, optical and near infrared spectral lines that are commonly used as
accretion tracers for T Tauri stars. The observed strengths of the Balmer
excesses have been reproduced from a magnetospheric accretion shock model,
providing a mean mass accretion rate of 1.11 x 10^-7 and 4.50 x 10^-7 Msun
yr^-1 for HD 31648 and HD 163296, respectively. Accretion rate variations are
observed, being more pronounced for HD 31648 (up to 0.5 dex). However, from the
comparison with previous results it is found that the accretion rate of HD
163296 has increased by more than 1 dex, on a timescale of ~ 15 years. Averaged
accretion luminosities derived from the Balmer excess are consistent with the
ones inferred from the empirical calibrations with the emission line
luminosities, indicating that those can be extrapolated to HAe stars. In spite
of that, the accretion rate variations do not generally coincide with those
estimated from the line luminosities, suggesting that the empirical
calibrations are not useful to accurately quantify accretion rate variability.Comment: 14 pages, 7 Figures, Accepted in Ap
Tracing the inner edge of the disk around HD 100546 with Ro-vibrational CO Emission Lines
In this paper we present high resolution 4.7micron spectra of the isolated
Herbig Be star HD100546. HD100546 has been the subject of intense scrutiny
because it is a young nearby star with a transitional disk. We observe the
Delta v=1 ro-vibrational CO transitions in order to clarify the distribution of
warm gas in the inner disk. Modeling of the CO spectrum indicates that the gas
is vibrationally excited by collisions and UV fluorescence. The observed
emission extends from 13-100AU. The inner edge of the molecular gas emission is
consistent with the inner edge of the optically thick dust disk indicating that
the inner hole is not simply a hole in the dust opacity but is likely cleared
of gas as well. The rotational temperature of the CO is ~1000K - much hotter
than the ~200K CO in the otherwise similar transitional disk surrounding
HD141569. The origin of this discrepancy is likely linked to the brighter PAH
emission observed toward HD100546. We use the excitation of the CO to constrain
the geometry of the inner disk and comment on the evolutionary state of the
system.Comment: 26 pages, 15 figures, Accepted by Ap
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