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[show abstract]
[hide abstract]
ABSTRACT: We present the spectral atlas of sources observed in low resolution with the Infrared Spectrograph on board the Spitzer Space Telescope. More than 11,000 distinct sources were extracted using a dedicated algorithm based on the SMART software with an optimal extraction (AdOpt package). These correspond to all 13,000 low-resolution observations of fixed objects (both single source and cluster observations). The pipeline includes image cleaning, individual exposure combination, and background subtraction. Particular attention is given to bad pixel and outlier rejection at the image and spectra levels. Most sources are spatially unresolved so that optimal extraction reaches the highest possible signal-to-noise ratio. For all sources, an alternative extraction is also provided that accounts for all of the source flux within the aperture. CASSIS provides publishable quality spectra through an online database together with several important diagnostics, such as the source spatial extent and a quantitative measure of detection level. Ancillary data such as available spectroscopic redshifts are also provided. The database interface will eventually provide various ways to interact with the spectra, such as on-the-fly measurements of spectral features or comparisons among spectra.
The Astrophysical Journal Supplement Series 08/2011; 196(1):8. · 13.46 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We present the spectral atlas of sources observed in low resolution with the
Infrared Spectrograph on board the Spitzer Space Telescope. More than 11,000
distinct sources were extracted using a dedicated algorithm based on the SMART
software with an optimal extraction (AdOpt package). These correspond to all
13,000 low resolution observations of fixed objects (both single source and
cluster observations). The pipeline includes image cleaning, individual
exposure combination, and background subtraction. A particular attention is
given to bad pixel and outlier rejection at the image and spectra levels. Most
sources are spatially unresolved so that optimal extraction reaches the highest
possible signal-to-noise ratio. For all sources, an alternative extraction is
also provided that accounts for all of the source flux within the aperture.
CASSIS provides publishable quality spectra through an online database together
with several important diagnostics, such as the source spatial extent and a
quantitative measure of detection level. Ancillary data such as available
spectroscopic redshifts are also provided. The database interface will
eventually provide various ways to interact with the spectra, such as
on-the-fly measurements of spectral features or comparisons among spectra.
08/2011;
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[show abstract]
[hide abstract]
ABSTRACT: We use WIRC, IR images of the Antennae (NGC 4038/4039) together with the extensive catalogue of 120 X-ray point sources (Zezas et al. 2006) to search for counterpart candidates. Using our proven frame-tie technique, we find 38 X-ray sources with IR counterparts, almost doubling the number of IR counterparts to X-ray sources first identified in Clark et al. (2007). In our photometric analysis, we consider the 35 IR counterparts that are confirmed star clusters. We show that the clusters with X-ray sources tend to be brighter, K_s ~16 mag, with (J-K_s) = 1.1 mag. We then use archival HST images of the Antennae to search for optical counterparts to the X-ray point sources. We employ our previous IR-to-X-ray frame-tie as an intermediary to establish a precise optical-to-X-ray frame-tie with <0.6 arcsec rms positional uncertainty. Due to the high optical source density near the X-ray sources, we determine that we cannot reliably identify counterparts. Comparing the HST positions to the 35 identified IR star cluster counterparts, we find optical matches for 27 of these sources. Using Bruzual-Charlot spectral evolutionary models, we find that most clusters associated with an X-ray source are massive, ~10^6 M_sun, young, ~10^6 yr, with moderate metallicities, Z=0.05. Comment: 9 page, 8 figures, accepted for publication in MNRAS
08/2010;
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[show abstract]
[hide abstract]
ABSTRACT: We present new advances in the spectral extraction of point-like sources adapted to the Infrared Spectrograph onboard the Spitzer Space Telescope. For the first time, we created a super-sampled point spread function of the low-resolution modules. We describe how to use the point spread function to perform optimal extraction of a single source and of multiple sources within the slit. We also examine the case of the optimal extraction of one or several sources with a complex background. The new algorithms are gathered in a plugin called Adopt which is part of the SMART data analysis software. Comment: Accepted for publication in PASP
10/2009;
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K. I. Uchida,
N. Calvet,
L. Hartmann,
F. Kemper,
W. J. Forrest,
D. M. Watson,
P. D'Alessio,
C. H. Chen,
E. Furlan,
B. Sargent,
B. R. Brandl,
T. L. Herter,
P. Morris,
P. C. Myers,
J. Najita,
G. C. Sloan, D. J. Barry,
J. Green,
L. D. Keller,
and P. Hall
[show abstract]
[hide abstract]
ABSTRACT: We have used the Spitzer Space Telescope Infrared Spectrograph to observe seven members of the TW Hya association, the nearest stellar association whose age (~10 Myr) is similar to the timescales thought to apply to planet formation and disk dissipation. Only two of the seven targets display infrared excess emission, indicating that substantial amounts of dust still exist closer to the stars than is characteristic of debris disks; however, in both objects we confirm an abrupt short-wavelength edge to the excess, as is seen in disks with cleared-out central regions. The mid-infrared excesses in the spectra of Hen 3-600 and TW Hya include crystalline silicate emission features, indicating that the grains have undergone significant thermal processing. We offer a detailed comparison between the spectra of TW Hya and Hen 3-600, and a model that corroborates the spectral shape and our previous understanding of the radial structure of these protoplanetary disks.
The Astrophysical Journal Supplement Series 12/2008; 154(1):439. · 13.46 Impact Factor
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M. Jura,
C. H. Chen,
E. Furlan,
J. Green,
B. Sargent,
W. J. Forrest,
D. M. Watson, D. J. Barry,
P. Hall,
T. L. Herter, [......],
K. Uchida,
P. D'Alessio,
B. R. Brandl,
L. D. Keller,
F. Kemper,
P. Morris,
J. Najita,
N. Calvet,
L. Hartmann,
and P. C. Myers
[show abstract]
[hide abstract]
ABSTRACT: We report spectra obtained with the Spitzer Space Telescope in the λ = 14-35 μm range of 19 nearby main-sequence stars with infrared excesses. The six stars with strong dust emission show no recognizable spectral features, suggesting that the bulk of the emitting particles have diameters larger than 10 μm. If the observed dust results from collisional grinding of larger solids, we infer minimum masses of the parent body population between 0.004 and 0.06 M⊕. We estimate grain production rates of ~1010 g s-1 around λ Boo and HR 1570; selective accretion of this matter may help explain their peculiar surface abundances. There appear to be inner truncations in the dust clouds at 48, 11, 52, and 54 AU around HR 333, HR 506, HR 1082, and HR 3927, respectively.
The Astrophysical Journal Supplement Series 12/2008; 154(1):453. · 13.46 Impact Factor
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W. J. Forrest,
B. Sargent,
E. Furlan,
P. D'Alessio,
N. Calvet,
L. Hartmann,
K. I. Uchida,
J. D. Green,
D. M. Watson,
C. H. Chen, [......],
L. D. Keller,
G. C. Sloan,
T. L. Herter,
B. R. Brandl,
J. R. Houck, D. J. Barry,
P. Hall,
P. W. Morris,
J. Najita,
and P. C. Myers
[show abstract]
[hide abstract]
ABSTRACT: We present the first Spitzer Space Telescope Infrared Spectrograph observations of the disks around classical T Tauri stars: spectra in the 5.2-30 μm range of six stars. The spectra are dominated by emission features from amorphous silicate dust, and a continuous component from 5 to 8 μm that in most cases comprises an excess above the photosphere throughout our spectral range. There is considerable variation in the silicate feature/continuum ratio, which implies variations of inclination, disk flaring, and stellar mass accretion rate. In most of our stars, structure in the silicate feature suggests the presence of a crystalline component. In one, CoKu Tau/4, no excess above the photosphere appears at wavelengths shortward of the silicate features, similar to 10 Myr old TW Hya, Hen 3-600, and HR 4796A. This indicates the optically thick inner disk is largely absent. The silicate emission features with peaks at 9.7 and 18 μm indicate small dust grains are present. The extremely low 10-20 μm color temperature of the dust excess, 135 K, indicates these grains are located more than 10 AU from the star. These features are suggestive of gravitational influence by planets or close stellar companions and grain growth in the region within 10 AU of the star, somewhat surprising for a star this young (1 Myr).
The Astrophysical Journal Supplement Series 12/2008; 154(1):443. · 13.46 Impact Factor
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Dan M. Watson,
F. Kemper,
Nuria Calvet,
Luke D. Keller,
Elise Furlan,
Lee Hartmann,
W. J. Forrest,
C. H. Chen,
Keven I. Uchida,
Joel D. Green, [......],
G. C. Sloan,
Terry L. Herter,
Bernhard R. Brandl,
J. R. Houck,
J. Najita,
Paola D'Alessio,
P. C. Myers, D. J. Barry,
P. Hall,
and P. W. Morris
[show abstract]
[hide abstract]
ABSTRACT: We present Spitzer Space Telescope Infrared Spectrograph observations in the 5.3-20 μm range of five young stellar objects in Taurus that have Class I continuum spectral energy distributions (λFλαλn, n ≥ 0), often taken to represent the youngest stellar objects in this star formation region. The spectra include a rich collection of broad absorption features that we identify with amorphous silicates and various ices, notably those of carbon dioxide and water. We show that the absorption features are produced mainly in the envelopes of these systems. The apparent depths of silicate and 15.2 μm CO2 ice features vary among the objects in a manner that is consistent with a variation of inclination with respect to the line of sight, contribution to the silicate features from material throughout the envelopes, and an origin for the CO2 ice feature in the outer parts of the envelope. Thus, these features provide new and useful constraints on models of the physical structure of Class I protostars.
The Astrophysical Journal Supplement Series 12/2008; 154(1):391. · 13.46 Impact Factor
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L. Armus,
V. Charmandaris,
H. W. W. Spoon,
J. R. Houck,
B. T. Soifer,
B. R. Brandl,
P. N. Appleton,
H. I. Teplitz,
S. J. U. Higdon,
D. W. Weedman, [......],
M. J. Burgdorf,
S. B. Fajardo-Acosta,
J. G. Ingalls,
J. Higdon,
L. Hao,
J. Bernard-Salas,
T. Herter,
J. Troeltzsch,
B. Unruh,
and M. Winghart
[show abstract]
[hide abstract]
ABSTRACT: We present spectra taken with the Infrared Spectrograph on the Spitzer Space Telescope covering the 5-38 μm region of three ultraluminous infrared galaxies (ULIRGs): Mrk 1014 (z = 0.163), Mrk 463 (z = 0.051), and UGC 5101 (z = 0.039). The continua of UGC 5101 and Mrk 463 show strong silicate absorption suggesting significant optical depths to the nuclei at 10 μm. UGC 5101 also shows the clear presence of water ice in absorption. Polycyclic aromatic hydrocarbon (PAH) emission features are seen in both Mrk 1014 and UGC 5101, including the 16.4 μm line in UGC 5101. The fine-structure lines are consistent with dominant active galactic nucleus (AGN) power sources in both Mrk 1014 and Mrk 463. In UGC 5101 we detect the [Ne V] 14.3 μm emission line, providing the first direct evidence for a buried AGN in the mid-infrared. The detection of the 9.66 μm and 17.03 μm H2 emission lines in both UGC 5101 and Mrk 463 suggest that the warm molecular gas accounts for 22% and 48% of the total molecular gas masses in these galaxies.
The Astrophysical Journal Supplement Series 12/2008; 154(1):178. · 13.46 Impact Factor
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J. R. Houck,
T. L. Roellig,
J. van Cleve,
W. J. Forrest,
T. Herter,
C. R. Lawrence,
K. Matthews,
H. J. Reitsema,
B. T. Soifer,
D. M. Watson, [......],
G. C. Sloan,
K. I. Uchida,
P. N. Appleton,
L. Armus,
M. J. Burgdorf,
S. B. Fajardo-Acosta,
C. J. Grillmair,
J. G. Ingalls,
P. W. Morris,
and H. I. Teplitz
[show abstract]
[hide abstract]
ABSTRACT: The Infrared Spectrograph (IRS) is one of three science instruments on the Spitzer Space Telescope. The IRS comprises four separate spectrograph modules covering the wavelength range from 5.3 to 38 μm with spectral resolutions, R = λ/Δλ ≈ 90 and 600, and it was optimized to take full advantage of the very low background in the space environment. The IRS is performing at or better than the prelaunch predictions. An autonomous target acquisition capability enables the IRS to locate the mid-infrared centroid of a source, providing the information so that the spacecraft can accurately offset that centroid to a selected slit. This feature is particularly useful when taking spectra of sources with poorly known coordinates. An automated data-reduction pipeline has been developed at the Spitzer Science Center.
The Astrophysical Journal Supplement Series 12/2008; 154(1):18. · 13.46 Impact Factor
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D. M. Clark,
M. H. Christopher,
S. S. Eikenberry,
B. R. Brandl,
J. C. Wilson,
J. C. Carson,
C. P. Henderson,
T. L. Hayward, D. J. Barry,
A. F. Ptak,
and E. J. M. Colbert
[show abstract]
[hide abstract]
ABSTRACT: In this Letter we report that a bright, X-ray source in the Antennae galaxies (NGC 4038/9), previously identified as an ultraluminous X-ray source (ULX), is in fact a background quasar. We identify an isolated infrared and optical counterpart within 03 ± 05 of the X-ray source X-37. After acquiring an optical spectrum of its counterpart, we use the narrow [O III] and broad Hα emission lines to identify X-37 as a quasar at a redshift of z = 0.26. Through a U, V, and Ks photometric analysis, we demonstrate that most of the observable light along this line of sight is from the quasar. We discuss the implications of this discovery and the importance of acquiring spectra for optical and IR counterparts to ULXs.
The Astrophysical Journal 12/2008; 631(2):L109. · 6.02 Impact Factor
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G. C. Sloan,
L. D. Keller,
W. J. Forrest,
E. Leibensperger,
B. Sargent,
A. Li,
J. Najita,
D. M. Watson,
B. R. Brandl,
C. H. Chen,
J. D. Green,
F. Markwick-Kemper,
T. L. Herter,
P. D'Alessio,
P. W. Morris, D. J. Barry,
P. Hall,
P. C. Myers,
and J. R. Houck
[show abstract]
[hide abstract]
ABSTRACT: We present spectra of four Herbig Ae/Be stars obtained with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope. All four of the sources show strong emission from polycyclic aromatic hydrocarbons (PAHs), with the 6.2 μm emission feature shifted to 6.3 μm and the strongest C–C skeletal-mode feature occurring at 7.9 μm instead of at 7.7 μm, as is often seen. Remarkably, none of the four stars has silicate emission. The strength of the 7.9 μm feature varies with respect to the 11.3 μm feature among the sources, indicating that we have observed PAHs with a range of ionization fractions. The ionization fraction is higher for systems with hotter and brighter central stars. Two sources, HD 34282 and HD 169142, show emission features from aliphatic hydrocarbons at 6.85 and 7.25 μm. The spectrum of HD 141569 shows a previously undetected emission feature at 12.4 μm that may be related to the 12.7 μm PAH feature. The spectrum of HD 135344, the coolest star in our sample, shows an unusual profile in the 7-9 μm region, with the peak emission to the red of 8.0 μm and no 8.6 μm PAH feature.
The Astrophysical Journal 12/2008; 632(2):956. · 6.02 Impact Factor
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S. S. Eikenberry,
K. Matthews,
J. L. LaVine,
M. A. Garske,
D. Hu,
M. A. Jackson,
S. G. Patel, D. J. Barry,
M. R. Colonno,
J. R. Houck,
J. C. Wilson,
S. Corbel,
and J. D. Smith
[show abstract]
[hide abstract]
ABSTRACT: We report near-infrared photometry, spectroscopy, and speckle imaging of the hot, luminous star we identify as candidate LBV 1806-20. We also present photometry and spectroscopy of three nearby stars, which are members of the same star cluster containing LBV 1806-20 and SGR 1806-20. The spectroscopy and photometry show that LBV 1806-20 is similar in many respects to the luminous "Pistol star," albeit with some important differences. They also provide estimates of the effective temperature and reddening of LBV 1806-20 and confirm distance estimates, leading to a best estimate for the luminosity of this star of greater than 5 × 106 L☉. The nearby cluster stars have spectral types and inferred absolute magnitudes that confirm the distance (and thus luminosity) estimate for LBV 1806-20. If we drop kinematic measurements of the distance (15.1 kpc), we have a lower limit on the distance of greater than 9.5 kpc and on the luminosity of greater than 2 × 106 L☉, based on the cluster stars. If we drop both the kinematic and cluster star indicators for distance, an ammonia absorption feature sets yet another lower limit to the distance of greater than 5.7 kpc, with a corresponding luminosity estimate of greater than 7 × 105 L☉ for the candidate LBV 1806-20. Furthermore, on the absis of very high angular resolution speckle images, we determine that LBV 1806-20 is not a cluster of stars but is rather a single star or binary system. Simple arguments based on the Eddington luminosity lead to an estimate of the total mass of LBV 1806-20 (single or binary) exceeding 190 M☉. We discuss the possible uncertainties in these results and their implications for the star formation history of this cluster.
The Astrophysical Journal 12/2008; 616(1):506. · 6.02 Impact Factor
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N. Calvet,
P. D'Alessio,
D. M. Watson,
R. Franco-Hernández,
E. Furlan,
J. Green,
P. M. Sutter,
W. J. Forrest,
L. Hartmann,
K. I. Uchida,
L. D. Keller,
B. Sargent,
J. Najita,
T. L. Herter, D. J. Barry,
and P. Hall
[show abstract]
[hide abstract]
ABSTRACT: We present Spitzer Infrared Spectrograph (IRS) observations of two objects of the Taurus population that show unambiguous signs of clearing in their inner disks. In one of the objects, DM Tau, the outer disk is truncated at 3 AU; this object is akin to another recently reported in Taurus, CoKu Tau/4, in that the inner disk region is free of small dust. Unlike CoKu Tau/4, however, this star is still accreting, so optically thin gas should still remain in the inner disk region. The other object, GM Aur, also accreting, has ~0.02 lunar masses of small dust in the inner disk region within ~5 AU, consistent with previous reports. However, the IRS spectrum clearly shows that the optically thick outer disk has an inner truncation at a much larger radius than previously suggested, ~24 AU. These observations provide strong evidence for the presence of gaps in protoplanetary disks.
The Astrophysical Journal 12/2008; 630(2):L185. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We use deep J (1.25 μm) and Ks (2.15 μm) images of the Antennae (NGC 4038/4039) obtained with the Wide-field InfraRed Camera on the Palomar 200 inch (5 m) telescope, together with the Chandra X-ray source list of Zezas and coworkers to search for infrared counterparts to X-ray point sources. We establish an X-ray/IR astrometric frame tie with ~0.5'' rms residuals over a ~4.3' field. We find 13 "strong" IR counterparts brighter than Ks = 17.8 mag and <1.0'' from X-ray sources, and an additional 6 "possible" IR counterparts between 1.0'' and 1.5'' from X-ray sources. Based on a detailed study of the surface density of IR sources near the X-ray sources, we expect only ~2 of the "strong" counterparts and ~3 of the "possible" counterparts to be chance superpositions of unrelated objects. Comparing both strong and possible IR counterparts to our photometric study of ~220 IR clusters in the Antennae, we find with a >99.9% confidence level that IR counterparts to X-ray sources are ΔMKs ~ 1.2 mag more luminous than average non-X-ray clusters. We also note that the X-ray/IR matches are concentrated in the spiral arms and "overlap" regions of the Antennae. This implies that these X-ray sources lie in the most "super" of the Antennae's super star clusters, and thus trace the recent massive star formation history here. Based on the NH inferred from the X-ray sources without IR counterparts, we determine that the absence of most of the "missing" IR counterparts is not due to extinction, but that these sources are intrinsically less luminous in the IR, implying that they trace a different (possibly older) stellar population. We find no clear correlation between X-ray luminosity classes and IR properties of the sources, although small-number statistics hamper this analysis.
The Astrophysical Journal 12/2008; 658(1):319. · 6.02 Impact Factor
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Lee Hartmann,
Nuria Calvet,
Dan M. Watson,
P. D'Alessio,
E. Furlan,
B. Sargent,
W. J. Forrest,
K. I. Uchida,
J. D. Green,
G. C. Sloan,
C. H. Chen,
J. Najita,
F. Kemper,
T. L. Herter,
P. Morris, D. J. Barry,
and P. Hall
[show abstract]
[hide abstract]
ABSTRACT: We present the infrared spectrum of the young binary system St 34 obtained with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope. The IRS spectrum clearly shows excess dust emission, consistent with the suggestion of White & Hillenbrand that St 34 is accreting from a circumbinary disk. The disk emission of St 34 is low in comparison with the levels observed in typical T Tauri stars; silicate features at ~10 and 20 μm are much weaker than typically seen in T Tauri stars; and excess emission is nearly absent at the shortest wavelengths observed (~5 μm). These features of the infrared spectrum suggest substantial grain growth (to eliminate silicate features) and possible settling of dust to the disk midplane (to reduce the continuum excess emission levels), along with a relatively evacuated inner disk, as expected due to gravitational perturbations by the binary system. Although the position of St 34 in the H-R diagram suggests an age of 8 ± 3 Myr, assuming that it lies at the distance of the Taurus-Auriga molecular clouds, White & Hillenbrand could not detect any Li I absorption, which would indicate a Li depletion age of roughly 25 Myr or more. We suggest that St 34 is closer than the Taurus clouds by ~ 30-40 pc and has an age roughly consistent with Li depletion models. Such an advanced age would make St 34 the oldest known low-mass pre-main-sequence object with a dusty accretion disk. The persistence of optically thick dust emission well outside the binary orbit may indicate a failure to make giant planets that could effectively remove dust particles.
The Astrophysical Journal 12/2008; 628(2):L147. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We present our early results of the mapping of the nucleus of the starburst galaxy NGC 253 and its immediate surroundings using the Infrared Spectrograph on board the Spitzer Space Telescope. The map is centered on the nucleus of the galaxy and spans the inner 800 × 688 pc2. The spatial distribution of the [Ne III] line at 15.55 μm and the polycyclic aromatic hydrocarbon feature at 11.3 μm peaks at the center, while the purely rotational transition of molecular hydrogen at 17.03 μm is strong over several slit positions. We perform a brief investigation of the implications of these measurements on the properties of the star formation in this region, using theories developed to explain the deficiency of massive stars in starbursts.
The Astrophysical Journal Supplement Series 12/2008; 154(1):242. · 13.46 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We use the previously-identified 15 infrared star-cluster counterparts to X-ray point sources in the interacting galaxies NGC 4038/4039 (the Antennae) to study the relationship between total cluster mass and X-ray binary number. This significant population of X-Ray/IR associations allows us to perform, for the first time, a statistical study of X-ray point sources and their environments. We define a quantity, \eta, relating the fraction of X-ray sources per unit mass as a function of cluster mass in the Antennae. We compute cluster mass by fitting spectral evolutionary models to K_s luminosity. Considering that this method depends on cluster age, we use four different age distributions to explore the effects of cluster age on the value of \eta and find it varies by less than a factor of four. We find a mean value of \eta for these different distributions of \eta = 1.7 x 10^-8 M_\sun^-1 with \sigma_\eta = 1.2 x 10^-8 M_\sun^-1. Performing a \chi^2 test, we demonstrate \eta could exhibit a positive slope, but that it depends on the assumed distribution in cluster ages. While the estimated uncertainties in \eta are factors of a few, we believe this is the first estimate made of this quantity to ``order of magnitude'' accuracy. We also compare our findings to theoretical models of open and globular cluster evolution, incorporating the X-ray binary fraction per cluster. Comment: 20 pages, 6 figures, accepted by ApJ
01/2008;
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G. C. Sloan,
M. Jura,
W. W. Duley,
K. E. Kraemer,
J. Bernard-Salas,
W. J. Forrest,
B. Sargent,
A. Li, D. J. Barry,
C. J. Bohac,
D. M. Watson,
J. R. Houck
[show abstract]
[hide abstract]
ABSTRACT: We have used the Infrared Spectrograph (IRS) on the Spitzer Space Telescope to obtain spectra of HD 100764, an apparently single carbon star with a circumstellar disk. The spectrum shows emission features from polycyclic aromatic hydrocarbons (PAHs) that are shifted to longer wavelengths than normally seen, as characteristic of ``class C'' systems in the classification scheme of Peeters et al. All seven of the known class C PAH sources are illuminated by radiation fields that are cooler than those which typically excite PAH emission features. The observed wavelength shifts are consistent with hydrocarbon mixtures containing both aromatic and aliphatic bonds. We propose that the class C PAH spectra are distinctive because the carbonaceous material has not been subjected to a strong ultraviolet radiation field, allowing relatively fragile aliphatic materials to survive. Comment: 11 pages (in emulateapj), 5 tables, 7 figures. Accepted for publication in ApJ
05/2007;
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[show abstract]
[hide abstract]
ABSTRACT: By the ejection of the outer parts of its envelope, a Planetary Nebula
(PN) contributes to the elemental enrichment of the interstellar medium.
PNe offer for the first time in the life of a star, the possibility to
reliably probe the products of the stellar nucleosynthesis. Furthermore,
the evolution and characteristics of the dust can also be studied. We
present the GTO program which has been designed to study a number of
planetary nebulae in the LMC and SMC. Preliminary results of the IRS
observations of planetary nebula LMC-SMP83 are also given.
11/2006; 357:157.
