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ABSTRACT: We present a mid-infrared high spectral resolution spectrum of CRL618 in the frequency ranges 778-784 and 1227-1249 cm^-1 (8.01-8.15 and 12.75-12.85 um) taken with the Texas Echelon-cross-Echelle Spectrograph (TEXES) and the Infrared Telescope Facility (IRTF). We have identified more than 170 ro-vibrational lines arising from C2H2, HCN, C4H2, and C6H2. We have found no unmistakable trace of C8H2. The line profiles display a complex structure suggesting the presence of polyacetylenes in several components of the circumstellar envelope (CSE). We derive total column densities of 2.5 10^17, 3.1 10^17, 2.1 10^17, 9.3 10^16 cm^-2, and < 5 10^16 cm^-2 for HCN, C2H2, C4H2, C6H2, and C8H2, respectively. The observations indicate that both the rotational and vibrational temperatures in the innermost CSE depend on the molecule, varying from 100 to 350 K for the rotational temperatures and 100 to 500 K for the vibrational temperatures. Our results support a chemistry in the innermost CSE based on radical-neutral reactions triggered by the intense UV radiation field. Comment: 9 pages, 4 figures, 1 table; accepted for publication in The Astrophysical Journal
11/2010;
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B. Sturm,
J. Bouwman,
Th. Henning,
N. J. Evans II,
B. Acke,
G. D. Mulders,
L. B. F. M. Waters,
E. F. van Dishoeck,
G. Meeus,
J. D. Green, [......],
C. Knez, J. H. Lacy,
J E Lee,
S. Maret,
R. Meijerink,
B. Merín,
L. Mundy,
K. M. Pontoppidan,
R. Visser,
U. A. Yíldíz
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ABSTRACT: We present far-infrared spectroscopic observations, taken with the Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory, of the protoplanetary disk around the pre-main-sequence star HD 100546. These observations are the first within the DIGIT Herschel key program, which aims to follow the evolution of dust, ice, and gas from young stellar objects still embedded in their parental molecular cloud core, through the final pre-main-sequence phases when the circumstellar disks are dissipated. Our aim is to improve the constraints on temperature and chemical composition of the crystalline olivines in the disk of HD 100546 and to give an inventory of the gas lines present in its far-infrared spectrum. The 69 \mu\m feature is analyzed in terms of position and shape to derive the dust temperature and composition. Furthermore, we detected 32 emission lines from five gaseous species and measured their line fluxes. The 69 \mu\m emission comes either from dust grains with ~70 K at radii larger than 50 AU, as suggested by blackbody fitting, or it arises from ~200 K dust at ~13 AU, close to the midplane, as supported by radiative transfer models. We also conclude that the forsterite crystals have few defects and contain at most a few percent iron by mass. Forbidden line emission from [CII] at 157 \mu\m and [OI] at 63 and 145 \mu\m, most likely due to photodissociation by stellar photons, is detected. Furthermore, five H2O and several OH lines are detected. We also found high-J rotational transition lines of CO, with rotational temperatures of ~300 K for the transitions up to J=22-21 and T~800 K for higher transitions.
05/2010;
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T. A. van Kempen,
J. D. Green,
N. J. Evans,
E. F. van Dishoeck,
L. E. Kristensen,
G. J. Herczeg,
B. Merin,
J E Lee,
J. K. J. Joergensen,
J. Bouwman, [......],
L. Mundy,
J. Najita,
J. Olofsson,
K. M. Pontoppidan,
C. Salyk,
B. Sturm,
R. Visser,
L. B. F. M. Waters,
C. Waelkens,
U. A. Yıldız
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ABSTRACT: DK Cha is an intermediate-mass star in transition from an embedded configuration to a star plus disk stage. We aim to study the composition and energetics of the circumstellar material during this pivotal stage. Using the Range Scan mode of PACS on the Herschel Space Observatory, we obtained a spectrum of DK Cha from 55 to 210 micron as part of the DIGIT Key Program. Almost 50 molecular and atomic lines were detected, many more than the 7 lines detected in ISO-LWS. Nearly the entire ladder of CO from J=14-13 to 38-37 (E_u/k = 4080 K), water from levels as excited as E_u/k = 843 K, and OH lines up to E_u/k = 290 K were detected. The continuum emission in our PACS SED scan matches the flux expected from a model consisting of a star, a surrounding disk of 0.03 Solar mass, and an envelope of a similar mass, supporting the suggestion that the object is emerging from its main accretion stage. Molecular, atomic, and ionic emission lines in the far-infrared reveal the outflow's influence on the envelope. The inferred hot gas can be photon-heated, but some emission could be due to C-shocks in the walls of the outflow cavity. Comment: 4 Page letter, To appear in A&A special issue on Herschel
05/2010;
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ABSTRACT: We present high resolution (R = 75,000-100,000) mid-infrared spectra of the
high-mass embedded young star IRS 1 in the NGC 7538 star-forming region.
Absorption lines from many rotational states of C2H2, 13C12CH2, CH3, CH4, NH3,
HCN, HNCO, and CS are seen. The gas temperature, column density, covering
factor, line width, and Doppler shift for each molecule are derived. All
molecules were fit with two velocity components between -54 and -63 km/s. We
find high column densities (~ 10e16 cm^2) for all the observed molecules
compared to values previously reported and present new results for CH3 and
HNCO. Several physical and chemical models are considered. The favored model
involves a nearly edge-on disk around a massive star. Radiation from dust in
the inner disk passes through the disk atmosphere, where large molecular column
densities can produce the observed absorption line spectrum.
02/2009;
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ABSTRACT: We report near-simultaneous interferometric measurements of the spectrum of Sagittarius A* over the 5-354 GHz range and single-dish observations that have yielded the first detection of Sgr A* at 850 GHz. We confirm that Sgr A*'s spectrum rises more steeply at short millimeter wavelengths than at centimeter wavelengths, leading to a near-millimeter/submillimeter excess that dominates its luminosity. Below 900 GHz, Sgr A*'s observed luminosity is 70 ± 30 L. A new upper limit to Sgr A*'s 24.3 μm flux, together with a compilation of other extant IR data, imply a far-infrared spectral turnover, which can result from either an intrinsic synchrotron cutoff or excess extinction near Sgr A*. If the former applies, Sgr A*'s total synchrotron luminosity is <103 L, while in the latter case it is <3 × 104 L if spherical symmetry also applies.
The Astrophysical Journal 01/2009; 490(1):L77. · 6.02 Impact Factor
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ABSTRACT: We present high-resolution (R= 90 000) mid-infrared spectra of M dwarfs. The mid-infrared region of the spectra of cool low-mass stars contains pure rotational water vapour transitions that may provide us with a new methodology in the determination of the effective temperatures for low-mass stars. We identify and assign water transitions in these spectra and determine how sensitive each pure rotational water transition is to small (25 K) changes in effective temperature. We find that, of the 36 confirmed and assigned pure rotational water transitions, at least 10 should be sensitive enough to be used as temperature indicators.
Monthly Notices of the Royal Astronomical Society 08/2008; 388(3):1305 - 1313. · 4.90 Impact Factor
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Martin A. Bitner,
M. J. Richter, J. H. Lacy,
D. T. Jaffe,
T. K. Greathouse,
G. J. Herczeg,
C. Salyk,
J. Najita,
G. A. Blake,
U. Gorti,
D. Hollenbach,
T. Currie,
J. S. Carr
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ABSTRACT: Over the past several years, we have undertaken a search for
mid-infrared pure rotational H2 emission from protoplanetary disks using
TEXES, the Texas Echelon Cross Echelle Spectrograph on both the IRTF
and, more recently, Gemini North. TEXES is a high spectral resolution,
mid-infrared spectrograph available to the astronomical community on
both the NASA IRTF and Gemini North telescopes. We gave highest priority
to observations of each target at both the J=3-1 (17.035 microns) and
J=4-2 (12.279 microns) settings. Sources with a detection at either
setting were followed up with observations at the J=6-4 (8.026 microns)
setting to constrain the temperature of the emitting gas. Flux ratios of
the three lines are sensitive to gas temperatures between 200 and 800 K.
We have observed 28 sources in at least one line including 8 Herbig
Ae/Be stars, 8 class I, 5 class II, 2 class III, 4 FU Ori, and 1 debris
disk and detected emission from 6/28. The lines we detect are generally
narrow (FWHM 10 km/s) and have small equivalent width. The high
spectral resolution available with TEXES, R 60,000 for J=3-1 and R
80,000 for J=4-2 and J=6-4, coupled with knowledge of the disk
inclination by other means allows us to estimate the radial location of
the emitting gas. Non-detections provide limits on the amount of warm
gas in regions where the dust is optically thin. Observations with TEXES
are supported by NSF grant AST-0607312.
11/2007; 39:872.
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ABSTRACT: We have used TEXES, the Texas Echelon-cross-Echelle Spectrograph on the
NASA Infrared Telescope Facility (IRTF) to search for pure rotational
H2 emission from young stars with disks. From the ground,
three pure rotational transitions of molecular hydrogen are accessible:
J = 6-4 (λ = 8.025 μm), J = 4-2 (λ = 12.27 μm), and
J = 3-1 (λ = 17.035 μm). Thus far, studies of gas in
protoplanetary disks have focused on either small radii using
near-infrared CO observations as a probe or on large radii with
observations in the millimeter wavelength range. Observations of
molecular emission in the mid-infrared offer the potential to study gas
in disks at intermediate radii (1-10 AU). Molecular hydrogen can be a
useful probe since it is the dominant constituent in disks and therefore
allows for mass determinations which avoid CO/H2 conversion
factors. When coupled with knowledge of the stellar mass and
inclination, high resolution observations (R ≈ 60,000 for J = 3-1 and
R ≈ 80,000 for J=4-2 and J = 6-4) may allow us to study line profiles
and determine the radial location of the emission. In the case of AB
Aurigae, we have detected J = 4-2 emission with FWHM of 7 km
s-1. Assuming an inclination of 20° and a stellar mass
of 2.5 Msun centers the emission at ≈16 AU in the disk.
08/2006; 352:229.
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ABSTRACT: The outer atmosphere of the M supergiant Betelgeuse is puzzling. Published observations of different kinds have shed light on different aspects of the atmosphere, but no unified picture has emerged. They have shown, for example, evidence of a water envelope (MOLsphere) that in some studies is found to be optically thick in the mid-infrared. In this paper, we present high-resolution, mid-infrared spectra of Betelgeuse recorded with the TEXES spectrograph. The spectra clearly show absorption features of water vapor and OH. We show that a spectrum based on a spherical, hydrostatic model photosphere with T_eff = 3600 K, an effective temperature often assumed for Betelgeuse, fails to model the observed lines. Furthermore, we show that published MOLspheres scenarios are unable to explain our data. However, we are able to model the observed spectrum reasonably well by adopting a cooler outer photospheric structure corresponding to T_mod = 3250 K. The success of this model may indicate the observed mid-infrared lines are formed in cool photospheric surface regions. Given the uncertainties of the temperature structure and the likely presence of inhomogeneities, we cannot rule out the possibility that our spectrum could be mostly photospheric, albeit non-classical. Our data put new, strong constraints on atmospheric models of Betelgeuse and we conclude that continued investigation requires consideration of non-classical model photospheres as well as possible effects of a MOLsphere. We show that the mid-infrared water-vapor features have great diagnostic value for the environments of K and M (super-) giant star atmospheres. Comment: Accepted by ApJ
10/2005;
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ABSTRACT: Using the Texas Echelon Cross Echelle Spectrograph (TEXES) we mapped emission in the H_2 v = 0-0 S(1) and S(2) lines toward the Orion Bar PDR at 2" resolution. We also observed H_2 v = 0-0 S(4) at selected points toward the front of the PDR. Our maps cover a 12" by 40" region of the bar where H_2 ro-vibrational lines are bright. The distributions of H_2 0-0 S(1), 0-0 S(2), and 1-0 S(1) line emission agree in remarkable detail. The high spatial resolution (0.002 pc) of our observations allows us to probe the distribution of warm gas in the Orion Bar to a distance approaching the scale length for FUV photon absorption. We use these new observational results to set parameters for the PDR models described in a companion paper (Draine et al. 2005, in prep). The best-fit model can account for the separation of the H_2 emission from the ionization front and the intensities of the ground state rotational lines as well as the 1-0 S(1) and 2-1 S(1) lines. This model requires significant adjustments to the commonly used values for the dust UV attenuation cross section and the photoelectric heating rate. Comment: 35 pages, 6 figures ApJ, accepted
05/2005;
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ABSTRACT: Using TEXES at NASA's 3m IRTF, we looked for H2 v=0,
J=3→1 and J=4→2 emission toward pre-main-sequence stars with
mostly null results. Some of our targets had previous reports of
H2 detections based on ISO observations. For more details on
these sources, see Richter et al. (2002). Here we concentrate on the
sources not observed by ISO.
11/2004; 324:232.
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ABSTRACT: Ultracompact HII regions are signposts of massive star formation and their properties provide diagnostics for the characteristics of very young O stars embedded in molecular clouds. While radio observations have given us a good picture of the morphology of these regions, they have not provided clear information about the kinematics. Using high spectral resolution observations of the 12.8 micron [NeII] line, it has been possible for the first time to trace the internal kinematics of several ultracompact HII regions. We find that the motions in the cometary ultracompact HII regions MonR2 and G29.96-0.02 are highly organized. The velocity patterns are consistent with parabolic ionized flows along a neutral boundary layer. Comment: 6 pages, 3 figures, to appear in the Proceedings of the ESO Workshop on High Resolution Infrared Spectroscopy in Astronomy, Garching, Germany 18-21 November 2003
03/2004;
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ABSTRACT: Hydrogen peroxide (H 2 O 2) has been suggested as a possible oxidizer of the martian surface. Photochemical models predict a mean column density in the range of 10 15 –10 16 cm −2 . However, a stringent upper limit of the H 2 O 2 abundance on Mars (9 × 10 14 cm −2) was derived in February 2001 from ground-based infrared spectroscopy, at a time corresponding to a maximum water vapor abundance in the northern summer (30 pr. µm, Ls = 112 •). Here we report the detection of H 2 O 2 on Mars in June 2003, and its mapping over the martian disk using the same technique, during the southern spring (Ls = 206 •) when the global water vapor abundance was ∼ 10 pr. µm. The spatial distribution of H 2 O 2 shows a maximum in the morning around the sub-solar latitude. The mean H 2 O 2 column density (6 × 10 15 cm −2) is significantly greater than our previous upper limit, pointing to seasonal variations. Our new result is globally consistent with the predictions of photochemical models, and also with submillimeter ground-based measurements obtained in September 2003 (Ls = 254 •), averaged over the martian disk (Clancy et al., 2004, Icarus 168, 116–121).
Icarus 01/2004; 170:424-429. · 3.38 Impact Factor
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ABSTRACT: We present the first observations of propane (C$_3$H$_8$) on Titan that unambiguously resolve propane features from other numerous stratospheric emissions. This is accomplished using a $R=\lambda/\delta\lambda\approx10^5$ spectrometer (TEXES) to observe propane's $\nu_{26}$ rotation-vibration band near 748 cm$^{-1}$. We find a best-fit fractional abundance of propane in Titan's stratosphere of $(6.2\pm1.2)\times10^{-7}$ in the altitude range to which we are sensitive (90-250 km or 13-0.24 mbar). Comment: accepted to ApJL 18 September 2003; See also: http://www.gps.caltech.edu/~hroe/propane2003/
09/2003;
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ABSTRACT: We present the first results of a study of the kinematics and morphology of ultracompact HII regions using a new observational technique. We used very high spatial (1.5") and spectral (3.4 km/s)resolution observations of the [NeII] line at 12.8 microns to study the ionized gas in Monoceros R2. The [NeII] emission shows an HII region with highest emission measure in a ~24" shell. Line widths are as narrow as 8 km/s at some positions. In places where the lines are complex and broader, the additional width is most likely due to overlap of narrower features along the line of sight. The global kinematics suggest that the 24" shell is expanding at ~10 km/s. However, the spectral profiles toward the southeast side of the shell are not consistent with a simple expansion picture. Comment: 25 pages, 7 figures
07/2003;
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ABSTRACT: We report detections of pure rotation lines of OH and H2O in the K1.5 III red-giant star Arcturus (alpha Bootis) using high-resolution, infrared spectra covering the regions 806-822 cm-1 (12.2-12.4 um) and 884-923 cm-1 (10.8-11.3 um). Arcturus is the hottest star yet to show water-vapor features in its disk-averaged spectrum. We argue that the water vapor lines originate from the photosphere, albeit in the outer layers. We are able to predict the observed strengths of OH and H2O lines satisfactorily after lowering the temperature structure of the very outer parts of the photosphere (log tau_500=-3.8 and beyond) compared to a flux-constant, hydrostatic, standard MARCS model photosphere. Our new model is consistently calculated including chemical equilibrium and radiative transfer from the given temperature structure. Possible reasons for a temperature decrease in the outer-most parts of the photosphere and the assumed break-down of the assumptions made in classical model-atmosphere codes are discussed. Comment: To appear in ApJ. See also http://www.astro.uu.se/~ryde/ART/
07/2002;
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ABSTRACT: We report on a limited search for pure-rotational molecular hydrogen emission associated with young, pre-main-sequence stars. We looked for H_2 v=0 J = 3->1 and J = 4->2 emission in the mid-infrared using the Texas Echelon-Cross-Echelle Spectrograph (TEXES) at NASA's 3m Infrared Telescope Facility. The high spectral and spatial resolution of our observations lead to more stringent limits on narrow line emission close to the source than previously achieved. One star, AB Aur, shows a possible (2sigma) H_2 detection, but further observations are required to make a confident statement. Our non-detections suggest that a significant fraction, perhaps all, of previously reported H_2 emission towards these objects could be extended on scales of 5" or more. Comment: 14 pages including 2 figures. Accepted by ApJ Letters
05/2002;
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ABSTRACT: We are building two high resolution, mid{infrared spectrographs; the Texas Echelon{cross{Echelle Spectrograph (TEXES) is designed for ground{based telescopes and the Echelon{cross{Echelle Spectrograph (EXES) is designed for the Stratospheric Observatory for Infrared Astronomy (SOFIA). Both spectrographs operate at 4-28 m in three spectroscopic modes: a cross{dispersed mode with R 10 , and longslit modes with either R 2 10 or R 4000. Both instruments use an echelon, a coarsely ruled, steeply blazed diraction grating, to achieve high resolution. These instruments will be well suited for the study of molecular lines in the cold interstellar medium, around young stars, and in planets.
01/2002;
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ABSTRACT: Hydrogen peroxide H 2 O 2 has been suggested as a possible oxidizer of the Martian surface. However, this minor species has never been detected. Photochemical models suggest that H 2 O 2 and H 2 O abundances should be correlated. We have searched for H 2 O 2 in the northern atmosphere of Mars, on Feb. 2–3, 2001 (Ls = 112 deg), at a time corresponding to maximum water vapor abundance in the northern hemisphere. The TEXES high-resolution grating spectrograph was used at the NASA/Infrared Telescope Facility (IRTF). Individual lines of the H 2 O 2 ν 6 band were searched for in the 1226–1235 cm −1 range (8.10–8.15 µm). Data were co-added for three different latitude sets: (1) full northern coverage (0–90 deg); (2) low northern latitudes (10–40 deg); (3) high northern latitudes (40–60 deg). From the absence of detectable H 2 O 2 lines in each of the three co-added data sets, we infer an H 2 O 2 2-σ upper limit of 9 × 10 14 cm −2 in the first case, 1.2 × 10 15 cm −2 in the second case, and 1.1 × 10 15 cm −2 in the third case. These numbers correspond to mean water vapor abundances of 30 pr-µm, 20 pr-µm and 40 pr-µm at the time of our observations. Our lowest upper limit is eight times lower than the value derived by Krasnopolsky et al. (1997) in the southern hemisphere in June 1988 (Ls = 222 deg); the mean water vapor abundance corresponding to their observation was 10 pr-µm. Our lowest upper limit is between 2.5 and 10 times lower than the values predicted by global photochemical models, also calculated for a mean H 2 O abundance of 10 pr-µm. In view of this, we have developed a new photochemical model which takes into account the actual geometry of the observations and the corresponding conditions of the water vapor abundance, dust and temperature in the Martian atmosphere, inferred from the MGS/TES data. Assuming an eddy diffusion coefficient of 10 7 cm 2 s −1 in the lower atmosphere, the calculated H 2 O 2 abundance is only a factor 1.5 greater than the observed upper limits.
A&A. 01/2002; 396:1037-1044.
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ABSTRACT: We present mid-infrared spectra of various hydrocarbons toward the hot core associated with the massive protostar NGC 7538 IRS 1. Because high abundances of fully hydrogenated molecules and saturated molecules are characteristic of hot cores, they provide laboratories in which to study interstellar chemistry. Through the study of C2H2, HCN, NH3, CH4, and CH3, we can constrain chemical models. We derive abundances for C2H2 and HCN and compare to model predictions. The observations were taken with the Texas Echelon Cross Echelle Spectrograph (TEXES)
Revista Mexicana de Astronomía y Astrofísica. 01/2002;
