[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. · 6.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Our view of extrasolar planetary systems was revolutionized in late 2008, when the first images of planets orbiting 50-100 AU from HR 8799 and Fomalhaut were announced. These results revealed the existence of giant extrasolar planets orbiting their host stars at distances comparable to the size of protoplanetary disks (100-500 AU). Despite their importance to understand the dynamics of the Kuiper belts of extrasolar systems, their possible role in the creation of transient debris disks, and the effects that these bodies can have on the stability of inner planets, little is known about the characteristics of planets at distances of 100 AU or more. To fill this gap, we propose to search for planetary mass companions around 23 young nearby stars. Thanks to the young age (
[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.
[Show abstract][Hide abstract] ABSTRACT: We compare the properties of warm dust emission from main-sequence A-type stars to those of dust around solar-type sources with similar Spitzer Space Telescope IRS/MIPS data and similar ages. Both samples have spectral energy distributions which show evidence of multiple components. Over the range of stellar types considered, we obtain nearly the same characteristic dust temperatures ( 190 K & 55 K for the inner & outer dust components respectively)--just above the ice line for the inner belts. The inner-belt temperature is readily explained if populations of grains are being released by sublimation of ice from icy planetesimals. Evaporation of comets at 170 K transports particles into an inner/warmer belt, where the super thermal grains left behind are found with Tdust >=190 K. 27 of the 50 A-type sources with warm excess are detected with Spitzer/MIPS at 70 µm (S/N > 3); the 50% rate of detection is comparable to the solar-type star sample where 9 of the 19 objects are also seen at MIPS 70 µm. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. Development of MIPS was funded by NASA through the Jet Propulsion Laboratory, subcontract 960785. This work was also partially supported by contract 1255094 from Caltech/JPL to the University of Arizona.
[Show abstract][Hide abstract] ABSTRACT: We are developing the Background-Limited Infrared-Submillimeter
Spectrograph (BLISS) for SPICA to provide a breakthrough capability for
far-IR survey spectroscopy. SPICAs large cold aperture allows mid-IR to
submm observations which are limited only by the natural backgrounds,
and BLISS is designed to operate near this fundamental limit.
BLISS-SPICA is 6 orders of magnitude faster than the spectrometers on
Herschel and SOFIA in obtaining full-band spectra. It enables
spectroscopy of dust-obscured galaxies at all epochs back to the rst
billion years after the Big Bang (redshift 6), and study of all stages
of planet formation in circumstellar disks. BLISS covers 35 - 433
microns range in ve or six wavelength bands, and couples two 2 sky
positions simultaneously. The instrument is cooled to 50 mK for optimal
sensitivity with an on-board refrigerators. The detector package is 4224
silicon-nitride micro-mesh leg-isolated bolometers with superconducting
transition-edge-sensed (TES) thermistors, read out with a cryogenic
time-domain multiplexer. All technical elements of BLISS have heritage
in mature scientic instruments, and many have own. We report on our
design study in which we are optimizing performance while accommodating
SPICAs constraints, including the stringent cryogenic mass budget. In
particular, we present our progress in the optical design and waveguide
spectrometer prototyping. A companion paper in Conference 7741 (Beyer et
al.) discusses in greater detail the progress in the BLISS TES bolometer
[Show abstract][Hide abstract] ABSTRACT: We present an overview of the calibration and properties of data from the IRAC instrument aboard the Spitzer Space Telescope taken after the depletion of cryogen. The cryogen depleted on 15 May 2009, and shortly afterward a two-month-long calibration and characterization campaign was conducted. The array temperature and bias setpoints were revised on 19 September 2009 to take advantage of lower than expected power dissipation by the instrument and to improve sensitivity. The final operating temperature of the arrays is 28.7 K, the applied bias across each detector is 500 mV and the equilibrium temperature of the instrument chamber is 27.55 K. The final sensitivities are essentially the same as the cryogenic mission with the 3.6 µm array being slightly less sensitive (10%) and the 4.5 µm array within 5% of the cryogenic sensitivity. The current absolute photometric uncertainties are 4% at 3.6 and 4.5 µm, and better than milli-mag photometry is achievable for long-stare photometric observations. With continued analysis, we expect the absolute calibration to improve to the cryogenic value of 3%. Warm IRAC operations fully support all science that was conducted in the cryogenic mission and all currently planned warm science projects (including Exploration Science programs). We expect that IRAC will continue to make ground-breaking discoveries in star formation, the nature of the early universe, and in our understanding of the properties of exoplanets.
[Show abstract][Hide abstract] ABSTRACT: Planetary Debris Disks provide unique insights to the formation and evolution of planetary systems similar to our own. Spitzer has brought studies of debris disks and late stages of planet formation into a new regime. Further breakthroughs will be greatly facilitated by assembling the existing data in a uniform and consistent way to determine the average behavior and to find deviant examples that can reveal critical steps in disk evolution. The existing data represent a potentially very important Spitzer legacy for the study of the origin and evolution of extrasolar systems, but they suffer from the following problems: 1.) inhomogeneous data reduction, 2.) inhomogeneous methods for photospheric predictions, leading to various thresholds adopted for identifying infrared excesses, and 3.) inaccurate and/or poorly-known stellar ages. Recently, improvements in data reduction and post-pipeline analysis, including a new method for dating solar-type stars, have been developed and tested thoroughly. In order to realize the legacy that these data represent, we propose to analyze and publish a debris disk catalog for thousands of stars consisting of completed observations in the cryogenic mission. With uniform and state-of-the-art data reduction and analysis approaches, our proposed program will provide a complete census on debris disk evolution around early- and late-type stars, guide plans for follow-up observations with future missions, and provide one of the fundamental legacies of Spitzer. Support for this work was provided by the NASA Astrophysics Data Analysis Program (ADP) program.
[Show abstract][Hide abstract] ABSTRACT: We use high spatial resolution IR data to investigate the origin of the silicate emission in a Seyfert 2 AGN and to probe the chemistry of the torus in NGC~1068. In NGC~2110, the closest known type 2 AGN with silicate emission features, mid-IR imaging and spectroscopy enable us to set tight constraints on the location of the emitting material (within 32 pc of the nucleus). Clumpy torus model fits to the data show that the silicate emission may arise in an edge-on torus. New L and M band spectra of NGC~1068 reveal the distribution of hydrocarbon absorption across the nucleus and set tighter limits on CO absorption features towards this AGN. Clumpy models of the dust screen might explain the lack of CO and the depth of the silicate feature, but the strength of the 3.4~mum feature, the presence of the silicate feature, and the absence of CO are strongly reminiscent of Galactic diffuse cloud environments.
[Show abstract][Hide abstract] ABSTRACT: We present a mid-infrared spectroscopic data cube of the central part of 30 Doradus, observed with Spitzer's Infrared Spectrograph and Multiband Imaging Photometer for Spitzer/spectral energy distribution mode. Aromatic dust emission features and emission lines from molecular and atomic hydrogen are detected but they are not particularly strong. The dominant spectral features are emission lines from moderately ionized species of argon, neon, and sulfur, which are used to determine the physical conditions in the ionized gas. The ionized gas excitation shows strong variations on parsec scales, some of which can plausibly be associated with individual hot stars. We fit the ionic line strengths with photoionization and shock models, and find that photoionization dominates in the region. The ionization parameter U traces the rim of the central bubble, as well as highlighting isolated sources of ionization, and at least one quiescent clump. The hardness of the ionizing radiation field T rad reveals several "hot spots" that are either the result of individual very hot stars or trace the propagation of the diffuse ionizing field through the surrounding neutral cloud. Consistent with other measurements of giant H II regions, log(U) ranges between –3 and –0.75, and T rad between 30,000 and 85,000 K.
The Astrophysical Journal 03/2009; 694(1):84. · 6.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The unified model of active galactic nuclei (AGN) predicts silicate emission features at 10 and 18 microns in type 1 AGN, and such features have now been observed in objects ranging from distant QSOs to nearby LINERs. More surprising, however, is the detection of silicate emission in a few type 2 AGN. By combining Gemini and Spitzer mid-infrared imaging and spectroscopy of NGC 2110, the closest known Seyfert 2 galaxy with silicate emission features, we can constrain the location of the silicate emitting region to within 32 pc of the nucleus. This is the strongest constraint yet on the size of the silicate emitting region in a Seyfert galaxy of any type. While this result is consistent with a narrow line region origin for the emission, comparison with clumpy torus models demonstrates that emission from an edge-on torus can also explain the silicate emission features and 2-20 micron spectral energy distribution of this object. In many of the best-fitting models the torus has only a small number of clouds along the line of sight, and does not extend far above the equatorial plane. Extended silicate-emitting regions may well be present in AGN, but this work establishes that emission from the torus itself is also a viable option for the origin of silicate emission features in active galaxies of both type 1 and type 2. Comment: ApJL, accepted
The Astrophysical Journal 02/2009; · 6.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: M dwarfs constitute 70% of the stars in our local neighborhood, yet we know little about the frequency and evolution of planetary systems for this diverse spectral class. Among the numerous M dwarfs sampled by Spitzer in the nearest 25pc, AU Mic remains a unique M dwarf with its debris disk, infrared excess, 12Myr age, flaring, and X-ray activity. We present results from 24 micron and 70 micron MIPS (Multiband Imaging Photometer for Spitzer) observations of 27 X-ray saturated M dwarfs like AU Mic out to an average distance of 30 pc. From these initial observations, we have discovered 3 new M dwarf debris disks identifiable from their infrared flux excess. We place our results in context with a sample of 70 A through M-type dwarfs selected with common youth indicators such as lithium abundance, moving group membership, chromospheric activity, and rapid rotation.
[Show abstract][Hide abstract] ABSTRACT: Spitzer and Caltech Submillimeter Observatory images and spectrophotometry of Eridani at wavelengths from 3.5 to 350 μm reveal new details of its bright debris disk. The 350 μm map confirms the presence of a ring at r = 11''-28''(35-90 AU), observed previously at longer sub-mm wavelengths. The Spitzer mid-IR and far-IR images do not show the ring, but rather a featureless disk extending from within a few arcsec of the star across the ring to r~ 34'' (110 AU). The spectral energy distribution (SED) of the debris system implies a complex structure. A model constrained by the surface brightness profiles and the SED indicates that the sub-mm ring emission is primarily from large (a~ 135 μm) grains, with smaller (a~ 15 μm) grains also present in and beyond the ring. The Spitzer Infrared Spectrograph and Multiband Imaging Photometer for Spitzer SED-mode spectrophotometry data clearly show the presence of spatially compact excess emission at λ 15 μm that requires the presence of two additional narrow belts of dust within the sub-mm ring's central void. The innermost belt at r~ 3 AU is composed of silicate dust. A simple dynamical model suggests that dust produced collisionally by a population of about 11 M ⊕ of planetesimals in the sub-mm ring could be the source of the emission from both in and beyond the sub-mm ring. Maintaining the inner belts and the inner edge to the sub-mm ring may require the presence of three planets in this system including the candidate radial velocity object.
The Astrophysical Journal 12/2008; 690(2):1522. · 6.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigate the luminous X-ray sources in the Lockman Hole (LH) and the extended Groth strip (EGS) detected at 24 μm using the Multiband Imaging Photometer (MIPS) and also with the Infrared Array Camera (IRAC) on board the Spitzer Space Telescope. We assemble optical/infrared spectral energy distributions (SEDs) for 45 X-ray/24 μm sources in the EGS and LH. Only about one-quarter of the hard X-ray/24 μm sources show pure type 1 active galactic nucleus (AGN) SEDs. More than half of the X-ray/24 μm sources have stellar emission-dominated or obscured SEDs, similar to those of local type 2 AGN and spiral/starburst galaxies. One-third of the sources detected in hard X-rays do not have a 24 μm counterpart. Two such sources in the LH have SEDs resembling those of S0/elliptical galaxies. The broad variety of SEDs in the optical-to-Spitzer bands of X-ray-selected AGNs means that AGNs selected according to the behavior in the optical/infrared will have to be supplemented by other kinds of data (e.g., X-ray) to produce unbiased samples of AGNs.
The Astrophysical Journal Supplement Series 12/2008; 154(1):155. · 16.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Massive clusters of galaxies are now recognized as very effective 'cosmic telescopes'. Because of the gravitational lensing effect, they can amplify significantly the background sources - by factors of a few tens - thereby bringing into view faint sources that would otherwise be unobservable. Note that in the background-limited case, which is applicable to IRAC observations, a factor of 20-30 gravitational amplification translates into increasing the integration time by a factor of 400-900. Because of this tremendous gain in sensitivity, IRAC imaging of lensing clusters will allow us to achieve JWST depth (~10 nJy) with Spitzer. Despite this great possibility, however, the full potential of the lensing cluster technique has not yet been realized due to the small number of clusters that have well-constrained accurate mass models. Here, we propose to conduct an IRAC imaging survey of 47 massive lensing clusters (5 hours/band, 2 bands) for which we have constructed accurate mass models through many years of intensive imaging/spectroscopic campaigns with HST, Keck, and VLT telescopes. This is the first time when such a large, statistical sample of clusters will be systematically employed to probe high-redshift Universe, and this proposed IRAC survey is a key component of our comprehensive program, which includes HST/WFC3 and Herschel observations starting next year. Scientifically, we will use the obtained IRAC data to (1) characterize z>6 galaxies (expecting ~50 z~7-8 galaxy detections), (2) support future Herschel and ALMA surveys, and (3) search for z>6 supernovae. The resultant data set will be a great legacy of Spitzer, allowing us to start tackling JWST sciences well before its launch.
[Show abstract][Hide abstract] ABSTRACT: Spitzer/IRAC in the warm mission is the only facility now existing or planned capable of carrying out an extensive, accurate time series photometric monitoring survey of star-forming regions in the thermal infrared. The demonstrated sensitivity and stability of IRAC allows measurement of the relative fluxes of YSO's down to the substellar mass limit to 1-2% accuracy in star-forming regions out to >500 pc. We propose a time series monitoring exploration science survey of the Orion Nebula Cluster and 11 very young, populous embedded star-forming cores which will provide >D 80 epochs of data for > 1500 YSO's. We will complement these observations with contemporaneous optical and near-IR monitoring data in order to allow comparison of the phase, amplitude and light-curve shape as a function of wavelength. These data will allow us to: (a) provide otherwise unobtainable constraints on the structure of the inner disks in Class I and II YSOs - and hence, perhaps, provide clues to the formation and migration of planets at young ages; (b) measure the short and long-term stability of hot spots on the surfaces of YSO's of all evolutionary stages; and (c) determine rotational periods for the largest sample to date of Class I YSO's and hence obtain the best measure of the initial angular momentum distribution of young stars.
[Show abstract][Hide abstract] ABSTRACT: Centaurus A is the nearest giant radio galaxy and provides an excellent opportunity for in depth study of an active galaxy. Believed to be the product of a recent merger of a elliptical and a spiral galaxy (resulting in a heavily absording dust lane), Cen A supports both star-formation as well as activity. Here we present IRAC, MIPS and IRS observations of Cen A and discuss the geometry of the warped dusty disk, the nature of IR emission associated with the radio jet and the relative strengths of spectral features as a function of position across the galaxy.
[Show abstract][Hide abstract] ABSTRACT: M dwarfs constitute ~70% of the stars in our local neighborhood, yet we know little about the frequency and evolution of debris disks and planetary systems for this diverse spectral class. We have discovered three new M dwarf debris disks with our Cycle-4 Spitzer program observing X-ray saturated, nearby, young M dwarfs. We propose to confirm the excesses with IRS observations, and to constrain disk properties from the SED. Combining our sample with previous Spitzer observations, we will constrain the age evolution, frequency, and dynamics of M dwarf debris disks to place into context disks around solar type stars.
[Show abstract][Hide abstract] ABSTRACT: M dwarfs constitute ~70% of the stars in our local neighborhood, yet we know little about the frequency and evolution of debris disks and planetary systems for this diverse spectral class. Among the numerous M dwarfs sampled by Spitzer in the nearest 25pc, AU Mic remains a unique M dwarf with its debris disk, infrared excess, 12Myr age, flaring, and X-ray activity (Chen et al. 2005, Plavchan et al. 2005, Kalas et al. 2005, Gautier et al., 2007). Plavchan et al. (2005) proposed that stellar wind drag can account for the apparent dearth of mature M dwarf debris disks. To test this hypothesis, in Cycle-4 we have observed to date 10 of 22 X-ray saturated M dwarfs like AU Mic out to a median distance of 32pc. From these initial observations, we have discovered 3 new M dwarf debris disks (Plavchan et al. in prep.). We propose to expand our sample to a statistically robust sample size comparable to the number of observed mature M dwarfs (~40). We propose observe 15 more nearby X-ray saturated M dwarfs in Cycle-5. These late-type dwarfs have ROSAT detections indicative of saturated X-ray activity (F_X>8x10^-5 ergs/cm^2/s) and are consequently likely to both be young and lack significant radial winds. Compared to the relatively old population of nearby M dwarfs, circumstellar disks are more likely to both exist and persist around these stars. Combining our sample with previous Spitzer observations, we will constrain the age evolution, frequency, and dynamics of M dwarf debris disks to place into context disks around solar type stars.
[Show abstract][Hide abstract] ABSTRACT: We present ~1000 new candidate Young Stellar Objects (YSOs) in the Large Magellanic Cloud selected from Spitzer Space Telescope data, as part of the Surveying the Agents of a Galaxy's Evolution (SAGE) Legacy program. The YSOs, detected by their excess infrared (IR) emission, represent early stages of evolution, still surrounded by disks and/or infalling envelopes. Previously, fewer than 20 such YSOs were known. The candidate YSOs were selected from the SAGE Point Source Catalog from regions of color-magnitude space least confused with other IR-bright populations. The YSOs are biased toward intermediate- to high-mass and young evolutionary stages, because these overlap less with galaxies and evolved stars in color-magnitude space. The YSOs are highly correlated spatially with atomic and molecular gas, and are preferentially located in the shells and bubbles created by massive stars inside. They are more clustered than generic point sources, as expected if star formation occurs in filamentary clouds or shells. We applied a more stringent color-magnitude selection to produce a subset of "high-probability" YSO candidates. We fitted the spectral-energy distributions (SEDs) of this subset and derived physical properties for those that were well fitted. The total mass of these well-fitted YSOs is ~2900 M_☉ and the total luminosity is ~2.1 × 10^6 L_☉ . By extrapolating the mass function with a standard initial mass function and integrating, we calculate a current star-formation rate of ~0.06 M_☉ yr^(–1), which is at the low end of estimates based on total ultraviolet and IR flux from the galaxy (~0.05 – 0.25 M_☉ yr^(–1)), consistent with the expectation that our current YSO list is incomplete. Follow-up spectroscopy and further data mining will better separate the different IR-bright populations and likely increase the estimated number of YSOs. The full YSO list is available as electronic tables, and the SEDs are available as an electronic figure for further use by the scientific community.
The Astronomical Journal 01/2008; · 4.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present a Spitzer IRS data cube of 30 Doradus and maps of fine-structure lines and PAH features derived from it. Analysis of the ionic lines of Ar, Ne, and S reveal physical conditions in the ionized gas at parsec-scale resolution. The prominent ridge in the center of the nebula shows elevated excitation, and several small-scale "hot spots" are revealed and analyzed. Hardening of the ionizing radiation field is detected in several interesting locations.
American Astronomical Society Meeting Abstracts; 12/2007