B. A. Whitney

Publications (67)113.58 Total impact

• Source

  Available from: Haley Louise Gomez

  Article: The Circumstellar Environment of R Coronae Borealis: White Dwarf Merger or Final Helium Shell Flash?

  Geoffrey C. Clayton, Ben E. K. Sugerman, S. Adam Stanford, B. A. Whitney, J. Honor, B. Babler, M. J. Barlow, K. D. Gordon, J. E. Andrews, T. R. Geballe, [......], G. Olofsson, E. Polehampton, H. L. Gomez, M Matsuura, P. C. Hargrave, R. J. Ivison, R. Wesson, S. J. Leeks, B. M. Swinyard, T. L. Lim
  [show abstract] [hide abstract]
  ABSTRACT: In 2007, R Coronae Borealis (R CrB) went into an historically deep and long decline. In this state, the dust acts like a natural coronagraph at visible wavelengths, allowing faint nebulosity around the star to be seen. Imaging has been obtained from 0.5 to 500 micron with Gemini/GMOS, HST/WFPC2, Spitzer/MIPS, and Herschel/SPIRE. Several of the structures around R CrB are cometary globules caused by wind from the star streaming past dense blobs. The estimated dust mass of the knots is consistent with their being responsible for the R CrB declines if they form along the line of sight to the star. In addition, there is a large diffuse shell extending up to 4 pc away from the star containing cool 25 K dust that is detected all the way out to 500 micron. The SED of R CrB can be well fit by a 150 AU disk surrounded by a very large diffuse envelope which corresponds to the size of the observed nebulosity. The total masses of the disk and envelope are 10^-4 and 2 M(Sun), respectively, assuming a gas-to-dust ratio of 100. The evidence pointing toward a white-dwarf merger or a final-helium-shell flash origin for R CrB is contradictory. The shell and the cometary knots are consistent with a fossil planetary nebula. Along with the fact that R CrB shows significant Lithium in its atmosphere, this supports the final-helium-shell flash. However, the relatively high inferred mass of R CrB and its high fluorine abundance support a white-dwarf merger.
  10/2011;
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  Available from: ArXiv

  Article: The Dust Properties of Two Hot R Coronae Borealis Stars and a Wolf-Rayet Central Star of a Planetary Nebula: in Search of a Possible Link

  Geoffrey C. Clayton, O. De Marco, B. A. Whitney, B. Babler, J. S. Gallagher, J. Nordhaus, A. K. Speck, M. J. Wolff, W. R. Freeman, K. A. Camp, W. A. Lawson, J. Roman-Duval, K. A. Misselt, M. Meade, G. Sonneborn, M Matsuura, M. Meixner
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  ABSTRACT: We present new Spitzer/IRS spectra of two hot R Coronae Borealis (RCB) stars, one in the Galaxy,V348 Sgr, and one lying in the LMC, HV 2671. These two objects may constitute a link between the RCB stars and the late Wolf-Rayet ([WCL]) class of central stars of planetary nebula (CSPNe) such as CPD -56 8032 that has little or no hydrogen in their atmospheres. HV 2671 and V348 Sgr are members of a rare subclass that has significantly higher effective temperatures than most RCB stars, but sharing the traits of hydrogen deficiency and dust formation that define the cooler RCB stars. The [WC] CSPNe star, CPD -56 8032, displays evidence for dual-dust chemistry showing both PAHs and crystalline silicates in its mid-IR spectrum. HV 2671 shows strong PAH emission but shows no sign of having crystalline silicates. The spectrum of V348 Sgr is very different from those of CPD -56 8032 and HV 2671. The PAH emission seen strongly in the other two stars is not present. Instead, the spectrum is dominated by a broad emission centered at about 8.2 micron. The mid-IR spectrum of CPD -56 8032 shows emission features that may be associated with C60. The other two stars do not show evidence for C60. HV 2671 has also been detected by Herschel/PACS and SPIRE. V348 Sgr and CPD -56 8032 have been detected by AKARI/FIS. These data were combined with Spitzer, IRAS, 2MASS and other photometry to produce their spectral energy distributions from the visible to the far-IR. Monte Carlo radiative transfer modeling was used to study the circumstellar dust around these stars. HV 2671 and CPD -56 8032 require both a flared inner disk with warm dust and an extended diffuse envelope with cold dust to to fit their SEDs. The SED of V348 Sgr can be fit with a much smaller disk and envelope.
  06/2011;
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  Available from: P. Riviere-Marichalar

  Article: Ysovar: The First Sensitive, Wide-area, Mid-infrared Photometric Monitoring of the Orion Nebula Cluster

  M. Morales-Calderón, J. R. Stauffer, L. A. Hillenbrand, R. Gutermuth, I. Song, L. M. Rebull, P. Plavchan, J. M. Carpenter, B. A. Whitney, K. Covey, [......], D. Barrado, K. Stapelfeldt, J. Hernández, L. E. Allen, D. R. Ardila, A. Bayo, F. Favata, D. James, M. Werner, and K. Wood
  [show abstract] [hide abstract]
  ABSTRACT: We present initial results from time-series imaging at infrared wavelengths of 0.9 deg2 in the Orion Nebula Cluster (ONC). During Fall 2009 we obtained 81 epochs of Spitzer 3.6 and 4.5 μm data over 40 consecutive days. We extracted light curves with ~3% photometric accuracy for ~2000 ONC members ranging from several solar masses down to well below the hydrogen-burning mass limit. For many of the stars, we also have time-series photometry obtained at optical (Ic ) and/or near-infrared (JK s ) wavelengths. Our data set can be mined to determine stellar rotation periods, identify new pre-main-sequence eclipsing binaries, search for new substellar Orion members, and help better determine the frequency of circumstellar disks as a function of stellar mass in the ONC. Our primary focus is the unique ability of 3.6 and 4.5 μm variability information to improve our understanding of inner disk processes and structure in the Class I and II young stellar objects (YSOs). In this paper, we provide a brief overview of the YSOVAR Orion data obtained in Fall 2009 and highlight our light curves for AA-Tau analogs—YSOs with narrow dips in flux, most probably due to disk density structures passing through our line of sight. Detailed follow-up observations are needed in order to better quantify the nature of the obscuring bodies and what this implies for the structure of the inner disks of YSOs.
  The Astrophysical Journal 05/2011; 733(1):50. · 6.02 Impact Factor
• Conference Proceeding: Simultaneous Spitzer/Chandra Observation Of Young Stellar Objects In GGD 12-15 - Do X-ray Flares Produce Disk Afterglows?

  J Forbrich, K ~R Covey, S ~J Wolk, J ~R Stauffer, R ~R ~A Gutermuth, M Morales Calderon, B ~A Whitney, J ~L Hora, B Posselt
  American Astronomical Society Meeting Abstracts #218; 05/2011
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  Available from: P. Riviere-Marichalar

  Article: YSOVAR: the first sensitive, wide-area, mid-IR photometric monitoring of the ONC

  M. Morales-Calderón, J. R. Stauffer, L. A. Hillenbrand, R. Gutermuth, I. Song, L. M. Rebull, P. Plavchan, J. M. Carpenter, B. A. Whitney, K. Covey, [......], D. Barrado, K. Stapelfeldt, J. Hernández, L. E. Allen, D. R. Ardila, A. Bayo, F. Favata, D. James, M Werner, K. Wood
  [show abstract] [hide abstract]
  ABSTRACT: We present initial results from time series imaging at infrared wavelengths of 0.9 sq. degrees in the Orion Nebula Cluster (ONC). During Fall 2009 we obtained 81 epochs of Spitzer 3.6 and 4.5 micron data over 40 consecutive days. We extracted light curves with ~3% photometric accuracy for ~2000 ONC members ranging from several solar masses down to well below the hydrogen burning mass limit. For many of the stars, we also have time-series photometry obtained at optical (Ic) and/or near-infrared (JKs) wavelengths. Our data set can be mined to determine stellar rotation periods, identify new pre-main-sequence (PMS) eclipsing binaries, search for new substellar Orion members, and help better determine the frequency of circumstellar disks as a function of stellar mass in the ONC. Our primary focus is the unique ability of 3.6 & 4.5 micron variability information to improve our understanding of inner disk processes and structure in the Class I and II young stellar objects (YSOs). In this paper, we provide a brief overview of the YSOVAR Orion data obtained in Fall 2009, and we highlight our light curves for AA-Tau analogs - YSOs with narrow dips in flux, most probably due to disk density structures passing through our line of sight. Detailed follow-up observations are needed in order to better quantify the nature of the obscuring bodies and what this implies for the structure of the inner disks of YSOs.
  03/2011;
• Article: SAGE-Spec Spitzer legacy program (Kemper+, 2010)

  F Kemper, P ~M Woods, V Antoniou, J -P Bernard, R ~D Blum, M ~L Boyer, J Chan, C -H ~R Chen, M Cohen, C Dijkstra, [......], A ~G ~G ~M Tielens, E Aarle, S ~D Dyk, J ~T Loon, H Winckel, U ~P Vijh, K Volk, B ~A Whitney, A ~N Wilkins, A ~A Zijlstra
  VizieR Online Data Catalog. 11/2010; 612:20683.
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  Available from: Jacco van Loon

  Article: Herschel Observations of a Newly Discovered UX Ori Star in the Large Magellanic Cloud

  Geoffrey C. Clayton, B. Sargent, M. L. Boyer, B. A. Whitney, Jacco Th. van Loon, M. Meixner, P. Tisserand, C. Engelbracht, S. Hony, R. Indebetouw, K. A. Misselt, K. Okumura, P. Panuzzo, J. Roman-Duval, M. Sauvage, J. M. Oliveira, M. Sewiło, and E. Churchwell
  [show abstract] [hide abstract]
  ABSTRACT: The LMC star, SSTISAGE1C J050756.44-703453.9, was first noticed during a survey of EROS-2 light curves for stars with large irregular brightness variations typical of the R Coronae Borealis (RCB) class. However, the visible spectrum showing emission lines including the Balmer and Paschen series as well as many Fe II lines is emphatically not that of an RCB star. This star has all of the characteristics of a typical UX Ori star. It has a spectral type of approximately A2 and has excited an H II region in its vicinity. However, if it is an LMC member, then it is very luminous for a Herbig Ae/Be star. It shows irregular drops in brightness of up to 2 mag, and displays the reddening and "blueing" typical of this class of stars. Its spectrum, showing a combination of emission and absorption lines, is typical of a UX Ori star that is in a decline caused by obscuration from the circumstellar dust. SSTISAGE1C J050756.44-703453.9 has a strong IR excess and significant emission is present out to 500 μm. Monte Carlo radiative transfer modeling of the spectral energy distribution requires that SSTISAGE1C J050756.44-703453.9 have both a dusty disk as well as a large extended diffuse envelope to fit both the mid- and far-IR dust emission. This star is a new member of the UX Ori subclass of the Herbig Ae/Be stars and only the second such star to be discovered in the LMC.
  The Astrophysical Journal 09/2010; 722(2):1131. · 6.02 Impact Factor
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  Available from: Eric Lagadec

  Article: The SAGE-Spec Spitzer Legacy program: The life-cycle of dust and gas in the Large Magellanic Cloud

  F. Kemper, Paul M. Woods, V. Antoniou, J. -P. Bernard, R. D. Blum, M. L. Boyer, J. Chan, C. -H. R. Chen, M Cohen, C. Dijkstra, [......], A. G. G. M. Tielens, E. van Aarle, S. D. Van Dyk, J. Th. van Loon, H. Van Winckel, Uma P. Vijh, K. Volk, B. A. Whitney, A. N. Wilkins, A. A. Zijlstra
  [show abstract] [hide abstract]
  ABSTRACT: The SAGE-Spec Spitzer Legacy program is a spectroscopic follow-up to the SAGE-LMC photometric survey of the Large Magellanic Cloud carried out with the Spitzer Space Telescope. We present an overview of SAGE-Spec and some of its first results. The SAGE-Spec program aims to study the life cycle of gas and dust in the Large Magellanic Cloud, and to provide information essential to the classification of the point sources observed in the earlier SAGE-LMC photometric survey. We acquired 224.6 hours of observations using the InfraRed Spectrograph and the SED mode of the Multiband Imaging Photometer for Spitzer. The SAGE-Spec data, along with archival Spitzer spectroscopy of objects in the Large Magellanic Cloud, are reduced and delivered to the community. We discuss the observing strategy, the specific data reduction pipelines applied and the dissemination of data products to the scientific community. Initial science results include the first detection of an extragalactic "21 um" feature towards an evolved star and elucidation of the nature of disks around RV Tauri stars in the Large Magellanic Cloud. Towards some young stars, ice features are observed in absorption. We also serendipitously observed a background quasar, at a redshift of z~0.14, which appears to be host-less. Comment: 33 pages, 12 figures, 8 tables; accepted for publication by PASP
  04/2010;
• Article: Lifting the Dusty Veil with Near- and Mid-Infrared Photometry. II. A Large-Scale Study of the Galactic Infrared Extinction Law

  G. Zasowski, S. R. Majewski, R. Indebetouw, M. R. Meade, D. L. Nidever, R. J. Patterson, B. Babler, M. F. Skrutskie, C. Watson, B. A. Whitney, and E. Churchwell
  [show abstract] [hide abstract]
  ABSTRACT: We combine near-infrared (Two Micron All Sky Survey) and mid-infrared (Spitzer-IRAC) photometry to characterize the IR extinction law (1.2-8 μm) over nearly 150° of contiguous Milky Way midplane longitude. The relative extinctions in five passbands across these wavelength and longitude ranges are derived by calculating color excess ratios for G and K giant red clump stars in contiguous midplane regions and deriving the wavelength dependence of extinction in each one. Strong, monotonic variations in the extinction law shape are found as a function of angle from the Galactic center, symmetric on either side of it. These longitudinal variations persist even when dense interstellar regions, known a priori to have a shallower extinction curve, are removed. The increasingly steep extinction curves toward the outer Galaxy indicate a steady decrease in the absolute-to-selective extinction ratio (RV ) and in the mean dust grain size at greater Galactocentric angles. We note an increasing strength of the 8 μm extinction inflection at high Galactocentric angles and, using theoretical dust models, show that this behavior is consistent with the trend in RV . Along several lines of sight where the solution is most feasible, A λ/AKs as a function of Galactic radius (R GC) is estimated and shown to have a Galactic radial dependence. Our analyses suggest that the observed relationship between extinction curve shape and Galactic longitude is due to an intrinsic dependence of the extinction law on Galactocentric radius.
  The Astrophysical Journal 11/2009; 707(1):510. · 6.02 Impact Factor
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  Available from: David L. Nidever

  Article: Lifting the Dusty Veil II: A Large-Scale Study of the Galactic Infrared Extinction Law

  G. Zasowski, S. R. Majewski, R. Indebetouw, M. R. Meade, D. L. Nidever, R. J. Patterson, B. Babler, M. F. Skrutskie, C. Watson, B. A. Whitney, E. Churchwell
  [show abstract] [hide abstract]
  ABSTRACT: We combine near-infrared (2MASS) and mid-infrared (Spitzer-IRAC) photometry to characterize the IR extinction law (1.2-8 microns) over nearly 150 degrees of contiguous Milky Way midplane longitude. The relative extinctions in 5 passbands across these wavelength and longitude ranges are derived by calculating color excess ratios for G and K giant red clump stars in contiguous midplane regions and deriving the wavelength dependence of extinction in each one. Strong, monotonic variations in the extinction law shape are found as a function of angle from the Galactic center, symmetric on either side of it. These longitudinal variations persist even when dense interstellar regions, known a priori to have a shallower extinction curve, are removed. The increasingly steep extinction curves towards the outer Galaxy indicate a steady decrease in the absolute-to-selective extinction ratio (R_V) and in the mean dust grain size at greater Galactocentric angles. We note an increasing strength of the 8 micron extinction inflection at high Galactocentric angles and, using theoretical dust models, show that this behavior is consistent with the trend in R_V. Along several lines of sight where the solution is most feasible, A_lambda/A_Ks as a function of Galactic radius is estimated and shown to have a Galactic radial dependence. Our analyses suggest that the observed relationship between extinction curve shape and Galactic longitude is due to an intrinsic dependence of the extinction law on Galactocentric radius. Comment: Accepted to ApJ
  10/2009;
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  Available from: arxiv.org

  Article: Mid-Infrared Variability of Protostars in IC 1396A

  M. Morales-Calderón, J. R. Stauffer, L. Rebull, B. A. Whitney, D. Barrado y Navascués, D. R. Ardila, I. Song, T. Y. Brooke, L. Hartmann, and N. Calvet
  [show abstract] [hide abstract]
  ABSTRACT: We have used Spitzer/Infrared Array Camera (IRAC) to conduct a photometric monitoring program of the IC1396A dark globule in order to study the mid-IR (3.6-8 μm) variability of the heavily embedded young stellar objects (YSOs) present in that area. We obtained light curves covering a 14 day timespan with a twice daily cadence for 69 YSOs, and continuous light curves with approximately 12 s cadence over 7 hr for 38 YSOs. Typical accuracies for our relative photometry were 1%-2% for the long timespan data and a few millimagnitude, corresponding to less than 0.5%, for the 7 hr continuous "staring-mode" data. More than half of the YSOs showed detectable variability, with amplitudes from ~0.05 mag to ~0.2 mag. About 30% of the YSOs showed quasi-sinusoidal light-curve shapes with apparent periods from 5 to 12 days and light-curve amplitudes approximately independent of wavelength over the IRAC bandpasses. We have constructed models which simulate the time-dependent spectral energy distributions of Class I and II YSOs in order to attempt to explain these light curves. Based on these models, the apparently periodic light curves are best explained by YSO models where one or two high-latitude photospheric spots heat the inner wall of the circumstellar disk, and where we view the disk at fairly large inclination angle. Disk inhomogeneities, such as increasing the height where the accretion funnel flows to the stellar hot spot, enhances the light-curve modulations. The other YSOs in our sample show a range of light-curve shapes, some of which are probably due to varying accretion rate or disk shadowing events. One star, IC1396A-47, shows a 3.5 hr periodic light curve; this object may be a PMS Delta Scuti star.
  The Astrophysical Journal 08/2009; 702(2):1507. · 6.02 Impact Factor
• Conference Proceeding: Early results from the SAGE-SMC Spitzer legacy

  K ~D Gordon, M Meixner, R ~D Blum, W Reach, B ~A Whitney, J Harris, R Indebetouw, A ~D Bolatto, J -P Bernard, M Sewilo, [......], H Shibai, J ~D Simon, L ~J Smith, S Srinivasan, A ~G ~G ~M Tielens, U ~P Vijh, S Dyk, J ~T Loon, K Volk, D Zaritsky
  IAU Symposium; 03/2009
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  Available from: ArXiv

  Article: IR Dust Bubbles II: Probing the Detailed Structure and Young Massive Stellar Populations of Galactic HII Regions

  C. Watson, T. Corn, E. B. Churchwell, B. L. Babler, M. S. Povich, M. R. Meade, B. A. Whitney
  [show abstract] [hide abstract]
  ABSTRACT: We present an analysis of late-O/early-B-powered, parsec-sized bubbles and associated star-formation using 2MASS, GLIMPSE, MIPSGAL and MAGPIS surveys. Three bubbles were selected from the Churchwell et al. (2007) catalog. We confirm that the structure identified in Watson et al. (2008) holds in less energetic bubbles, i.e. a PDR, identified by 8 um emission due to PAHs surrounds hot dust, identified by 24 um emission and ionized gas, identified by 20 cm continuum. We estimate the dynamical age of two bubbles by comparing bubble sizes to numerical models of Hosokawa & Inutsuka (2006). We also identify and analyze candidate young stellar objects (YSOs) using SED fitting and identify sites of possible triggered star-formation. Lastly, we identify likely ionizing sources for two sources based on SED fitting.
  01/2009;
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  Available from: bu.edu

  Article: The Bubbling Galactic Disk

  E. Churchwell, M. S. Povich, D Allen, M. G. Taylor, M. R. Meade, B. L. Babler, R. Indebetouw, C. Watson, B. A. Whitney, M. G. Wolfire, [......], M Cohen, C. J. Cyganowski, J. M. Jackson, H. A. Kobulnicky, J. S. Mathis, E. P. Mercer, S. R. Stolovy, B. Uzpen, D. F. Watson, M. J. Wolff
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  ABSTRACT: A visual examination of the images from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) has revealed 322 partial and closed rings that we propose represent partially or fully enclosed three-dimensional bubbles. We argue that the bubbles are primarily formed by hot young stars in massive star formation regions. We have found an average of about 1.5 bubbles per square degree. About 25% of the bubbles coincide with known radio H II regions, and about 13% enclose known star clusters. It appears that B4-B9 stars (too cool to produce detectable radio H II regions) probably produce about three-quarters of the bubbles in our sample, and the remainder are produced by young O-B3 stars that produce detectable radio H II regions. Some of the bubbles may be the outer edges of H II regions where PAH spectral features are excited and may not be dynamically formed by stellar winds. Only three of the bubbles are identified as known SNRs. No bubbles coincide with known planetary nebulae or W-R stars in the GLIMPSE survey area. The bubbles are small. The distribution of angular diameters peaks between 1' and 3' with over 98% having angular diameters less than 10' and 88% less than 4'. Almost 90% have shell thicknesses between 0.2 and 0.4 of their outer radii. Bubble shell thickness increases approximately linearly with shell radius. The eccentricities are rather large, peaking between 0.6 and 0.7; about 65% have eccentricities between 0.55 and 0.85.
  The Astrophysical Journal 12/2008; · 6.02 Impact Factor
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  Available from: arxiv.org

  Article: First GLIMPSE Results on the Stellar Structure of the Galaxy

  R. A. Benjamin, E. Churchwell, B. L. Babler, R. Indebetouw, M. R. Meade, B. A. Whitney, C. Watson, M. G. Wolfire, M. J. Wolff, R. Ignace, [......], D. P. Clemens, L. Chomiuk, M. Cohen, J. M. Dickey, J. M. Jackson, H. A. Kobulnicky, E. P. Mercer, J. S. Mathis, S. R. Stolovy, and B. Uzpen
  [show abstract] [hide abstract]
  ABSTRACT: The GLIMPSE (Galactic Legacy Mid-Plane Survey Extraordinaire) Point Source Catalog of ~30 million mid-infrared sources toward the inner Galaxy, 10° ≤ |l| ≤ 65° and |b| ≤ 1°, was used to determine the distribution of stars in Galactic longitude, l, latitude, b, and apparent magnitude, m. The counts versus longitude can be approximated by the modified Bessel function N = N0(l/l0)K1(l/l0), where l0 is insensitive to limiting magnitude, band choice, and side of Galactic center: l0 = 17°-30° with a best-fit value in the 4.5 μm band of l0 = 24° ± 4°. Modeling the source distribution as an exponential disk yields a radial scale length of H* = 3.9 ± 0.6 kpc. There is a pronounced north-south asymmetry in source counts for |l| 30°, with ~25% more stars in the north. For l = 10°-30°, there is a strong enhancement of stars of m = 11.5-13.5 mag. A linear bar passing through the Galactic center with half-length Rbar = 4.4 ± 0.5 kpc, tilted by = 44° ± 10° to the Sun-Galactic center line, provides the simplest interpretation of these data. We examine the possibility that enhanced source counts at l = 26°-28°, 315-34°, and 306°-309° are related to Galactic spiral structure. Total source counts are depressed in regions where the counts of red objects (mK-m[8.0] > 3) peak. In these areas, the counts are reduced by extinction due to molecular gas, high diffuse backgrounds associated with star formation, or both.
  The Astrophysical Journal 12/2008; 630(2):L149. · 6.02 Impact Factor
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  Available from: arxiv.org

  Article: A GLIMPSE of Star Formation in the Giant H II Region RCW 49

  B. A. Whitney, R. Indebetouw, B. L. Babler, M. R. Meade, C. Watson, M. J. Wolff, M. G. Wolfire, D. P. Clemens, T. M. Bania, R. A. Benjamin, [......], J. M. Dickey, F. Heitsch, J. M. Jackson, H. A. Kobulnicky, A. P. Marston, J. S. Mathis, E. P. Mercer, J. R. Stauffer, S. R. Stolovy, and E. Churchwell
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  ABSTRACT: GLIMPSE imaging using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope indicates that star formation is ongoing in the RCW 9 giant H II region. A photometric comparison of the sources in RCW 49 to a similar area to its north finds that at least 300 stars brighter than 13th magnitude in band [3.6] have infrared excesses inconsistent with reddening due to foreground extinction. These are likely young stellar objects (YSOs) more massive than 2.5 M, suggesting that thousands more low-mass stars are forming in this cloud. Some of the YSOs are massive (B stars) and therefore very young, suggesting that a new generation of star formation is occurring, possibly triggered by stellar winds and shocks generated by the older (2-3 Myr) central massive cluster. The Spitzer IRAC camera has proven to be ideally suited for distinguishing young stars from field stars, and the GLIMPSE survey of the Galactic plane will likely find thousands of new star formation regions.
  The Astrophysical Journal Supplement Series 12/2008; 154(1):315. · 13.46 Impact Factor
• Article: The Wavelength Dependence of Interstellar Extinction from 1.25 to 8.0 μm Using GLIMPSE Data

  R. Indebetouw, J. S. Mathis, B. L Babler, M. R. Meade, C. Watson, B. A. Whitney, M. J. Wolff, M. G. Wolfire, M. Cohen, T. M. Bania, R. A. Benjamin, D. P. Clemens, J. M. Dickey, J. M. Jackson, H. A. Kobulnicky, A. P. Marston, E. P. Mercer, J. R. Stauffer, S. R. Stolovy, and E. Churchwell
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  ABSTRACT: We determine and tabulate A[λ]/AK, the wavelength dependence of interstellar extinction, in the Galactic plane for 1.25 μm ≤ λ ≤ 8.0 μm along two lines of sight: l = 42° and 284°. The first is a relatively quiescent and unremarkable region; the second contains the giant H II region RCW 49, as well as a "field" region unrelated to the cluster and nebulosity. Areas near these Galactic longitudes were imaged at J, H, and K bands by 2MASS and at 3-8 μm by Spitzer for the GLIMPSE Legacy program. We measure the mean values of the color excess ratios (A[λ] - AK)/(AJ - AK) directly from the color distributions of observed stars. The extinction ratio between two of the filters, e.g., AJ/AK, is required to calculate A[λ]/AK from those measured ratios. We use the apparent JHK magnitudes of giant stars along our two sight lines and fit the reddening as a function of magnitude (distance) to determine AJ kpc-1, AK kpc-1, and AJ/AK. Our values of A[λ]/AK show a flattening across the 3-8 μm wavelength range, roughly consistent with the extinction measurements derived by Lutz and coworkers for the sight line toward the Galactic center.
  The Astrophysical Journal 12/2008; 619(2):931. · 6.02 Impact Factor
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  Available from: bu.edu

  Article: RCW 49 at Mid-Infrared Wavelengths: A GLIMPSE from the Spitzer Space Telescope

  E. Churchwell, B. A. Whitney, B. L. Babler, R. Indebetouw, M. R. Meade, Christer Watson, M. J. Wolff, M. G. Wolfire, T. M. Bania, R. A. Benjamin, [......], K. E. Devine, J. M. Dickey, F. Heitsch, J. M. Jackson, H. A. Kobulnicky, A. P. Marston, J. S. Mathis, E. P. Mercer, J. R. Stauffer, and S. R. Stolovy
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  ABSTRACT: The luminous, massive star formation region RCW 49, located in the southern Galactic plane, was imaged with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope as part of the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) program. The IRAC bands contain polycyclic aromatic hydrocarbon (PAH) features at 3.3, 6.2, 7.7, and 8.6 μm, as well as the Brα line. These features are the major contributors to the diffuse emission from RCW 49 in the IRAC bands. The Spitzer IRAC images show that the dust in RCW 49 is distributed in a network of fine filaments, pillars, knots, sharply defined boundaries, bubbles, and bow shocks. The regions immediately surrounding the ionizing star cluster and W-R stars are evacuated of dust by stellar winds and radiation. The IRAC images of RCW 49 suggest that the dust in RCW 49 has been sculpted by the winds and radiation from the embedded luminous stars in the inner 5' (inner ~6 pc) of the nebula. At projected angular radii > 5' from the central ionizing cluster, the azimuthally averaged infrared intensity falls off as ~-3. Both high-resolution radio and mid-IR images suggest that the nebula is density bounded along its western boundary. The filamentary structure of the dust in RCW 49 suggests that the nebula has a small dust filling factor and, as a consequence, the entire nebula may be slightly density bounded to H-ionizing photons.
  The Astrophysical Journal Supplement Series 12/2008; 154(1):322. · 13.46 Impact Factor
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  Available from: bu.edu

  Article: New Star Clusters Discovered in the GLIMPSE Survey

  E. P. Mercer, D. P. Clemens, M. R. Meade, B. L. Babler, R. Indebetouw, B. A. Whitney, C. Watson, M. G. Wolfire, M. J. Wolff, T. M. Bania, R. A. Benjamin, M. Cohen, J. M. Dickey, J. M. Jackson, H. A. Kobulnicky, J. S. Mathis, J. R. Stauffer, S. R. Stolovy, B. Uzpen, and E. B. Churchwell
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  ABSTRACT: A systematic and automated search of the extensive GLIMPSE mid-infrared survey data of the inner Galaxy was carried out to uncover new star clusters. This search has yielded 59 new clusters. Using our automated search algorithm, these clusters were identified as significant localized overdensities in the GLIMPSE point-source catalog (GLMC) and archive (GLMA). Subsequent visual inspection of the GLIMPSE image mosaics confirmed the existence of these clusters plus an additional 33 heavily embedded clusters missed by our detection algorithm, for a total of 92 newly discovered clusters. These previously uncataloged clusters range in type from heavily embedded to fully exposed clusters. More than half of the clusters have memberships exceeding 35 stars, and nearly all the clusters have diameters of 3' or less. The Galactic latitude distribution of the clusters reveals that the majority are concentrated toward the Galactic midplane. There is an asymmetry in the number of clusters located above and below the midplane, with more clusters detected below the midplane. We also observe an asymmetry in the number of clusters detected in the northern and southern halves of the Galaxy, with more than twice as many clusters detected in the south.
  The Astrophysical Journal 12/2008; 635(1):560. · 6.02 Impact Factor
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  Available from: arxiv.org

  Article: The Frequency of Mid-Infrared Excess Sources in Galactic Surveys

  B. Uzpen, H. A. Kobulnicky, A. J. Monson, M. J. Pierce, D. P. Clemens, D. E. Backman, M. R. Meade, B. L. Babler, R. Indebetouw, B. A. Whitney, [......], J. S. Mathis, E. P. Mercer, M. S. Povich, J. Rho, T. P. Robitaille, M. Sewilo, S. R. Stolovy, D. F. Watson, M. J. Wolff, and E. Churchwell
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  ABSTRACT: We have identified 230 Tycho-2 Spectral Catalog stars that exhibit 8 μm mid-IR extraphotospheric excesses in the MSX and Spitzer GLIMPSE surveys. Of these, 183 are either OB stars earlier than B8 in which the excess plausibly arises from a thermal bremsstrahlung component or evolved stars in which the excess may be explained by an atmospheric dust component. The remaining 47 stars have spectral classifications B8 or later and appear to be main-sequence or late pre-main-sequence objects harboring circumstellar disks. Six of the 47 stars exhibit multiple signatures characteristic of pre-main-sequence circumstellar disks, including emission lines, near-IR K-band excesses, and X-ray emission. Approximately one-third of the remaining 41 sources have emission lines suggesting relative youth. We modeled the excesses in 26 stars having two or more measurements in excess of the expected photospheres as single-component blackbodies. We determine probable disk temperatures and fractional IR luminosities in the range 191 K < T < 787 K and 3.9 × 10-4 < LIR/L* < 2.7 × 10-1. The majority of our modeled sample (14 stars) have 10-3 < LIR/L* < 10-2 and are consistent with either transition disks or massive debris disks. These objects have fractional IR luminosities and temperatures between those of β Pic-type debris disk systems (LIR/L* ≤ 10-3) and Class II pre-main-sequence systems (LIR/L* 10-1). We estimate a lower limit on the fraction of Tycho-2 Spectral Catalog main-sequence stars having mid-IR, but not near-IR, excesses to be 1.0% ± 0.3%.
  The Astrophysical Journal 12/2008; 658(2):1264. · 6.02 Impact Factor