Publications (86)32.53 Total impact
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Article: HST FUV C IV observations of the hot DG Tauri jet
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ABSTRACT: Protostellar jets are tightly connected to the accretion process and regulate the angular momentum balance of accreting star-disk systems. The DG Tau jet is one of the best-studied protostellar jets and contains plasma with temperatures ranging over three orders of magnitude within the innermost 50 AU of the jet. We present new Hubble Space Telescope (HST) far ultraviolet (FUV) long-slit spectra spatially resolving the C IV emission (T~1e5 K) from the jet for the first time, and quasi-simultaneous HST observations of optical forbidden emission lines ([O I], [N II], [S II] and [O III]) and fluorescent H2 lines. The C IV emission peaks at 42 AU from the stellar position and has a FWHM of 52 AU along the jet. Its deprojected velocity of around 200 km/s decreases monotonically away from the driving source. In addition, we compare our HST data with the X-ray emission from the DG Tau jet. We investigate the requirements to explain the data by an initially hot jet compared to local heating. Both scenarios indicate a mass loss by the T~1e5 K jet of ~1e-9 Msun/year, i.e., between the values for the lower temperature jet (T~1e4 K) and the hotter X-ray emitting part (T>1e6 K). However, a simple initially hot wind requires a large launching region (~1 AU), and we therefore favor local heating.12/2012; -
Dataset: ORIGIN expAstr11
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Conference Proceeding: METIS: the thermal infrared instrument for the E-ELT
Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series; 09/2012 -
Article: On the origin of [Ne II] emission in young stars: mid-infrared and optical observations with the Very Large Telescope
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ABSTRACT: {Abridged version for ArXiv}. We provide direct constraints on the origin of the [Ne II] emission in 15 young stars using high-spatial and spectral resolution observations with VISIR at the VLT that allow us to study the kinematics of the emitting gas. In addition we compare the [Ne II] line with optical forbidden lines observed for three stars with UVES. The [Ne II] line was detected in 7 stars, among them the first confirmed detection of [Ne II] in a Herbig Be star, V892 Tau. In four cases, the large blueshifted lines indicate an origin in a jet. In two stars, the small shifts and asymmetric profiles indicate an origin in a photo-evaporative wind. CoKu Tau 1, seen close to edge-on, shows a spatially unresolved line centered at the stellar rest velocity, although cross-dispersion centroids move within 10 AU from one side of the star to the other as a function of wavelength. The line profile is symmetric with wings extending up to about +-80 km/s. The origin of the [Ne II] line could either be due to the bipolar jet or to the disk. For the stars with VLT-UVES observations, in several cases, the optical forbidden line profiles and shifts are very similar to the profile of the [Ne II] line, suggesting that the lines are emitted in the same region. A general trend observed with VISIR is a lower line flux when compared with the fluxes obtained with Spitzer. We found no correlation between the line full-width at half maximum and the line peak velocity. The [Ne II] line remains undetected in a large part of the sample, an indication that the emission detected with Spitzer in those stars is likely extended.05/2012; -
Article: ORIGIN: metal creation and evolution from the cosmic dawn
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ABSTRACT: ORIGIN is a proposal for the M3 mission call of ESA aimed at the study of metal creation from the epoch of cosmic dawn. Using high-spectral resolution in the soft X-ray band, ORIGIN will be able to identify the physical conditions of all abundant elements between C and Ni to red-shifts of z = 10, and beyond. The mission will answer questions such as: When were the first metals created? How does the cosmic metal content evolve? Where do most of the metals reside in the Universe? What is the role of metals in structure formation and evolution? To reach out to the early Universe ORIGIN will use Gamma-Ray Bursts (GRBs) to study their local environments in their host galaxies. This requires the capability to slew the satellite in less than a minute to the GRB location. By studying the chemical composition and properties of clusters of galaxies we can extend the range of exploration to lower redshifts (z ∼0.2). For this task we need a high-resolution spectral imaging instrument with a large field of view. Using the same instrument, we can also study the so far only partially detected baryons in the Warm-Hot Intergalactic Medium (WHIM). The less dense part of the WHIM will be studied using absorption lines at low redshift in the spectra for GRBs. The ORIGIN mission includes a Transient Event Detector (coded mask with a sensitivity of 0.4 photon/cm2/s in 10s in the 5–150keV band) to identify and localize 2000GRBs over a five year mission, of which ∼65GRBs have a redshift >7. The Cryogenic Imaging Spectrometer, with a spectral resolution of 2.5eV, a field of view of 30arcmin and large effective area below 1keV has the sensitivity to study clusters up to a significant fraction of the virial radius and to map the denser parts of the WHIM (factor 30 higher than achievable with current instruments). The payload is complemented by a Burst InfraRed Telescope to enable onboard red-shift determination of GRBs (hence securing proper follow up of high-z bursts) and also probes the mildly ionized state of the gas. Fast repointing is achieved by a dedicated Controlled Momentum Gyro and a low background is achieved by the selected low Earth orbit. KeywordsX-ray–Mission–Gamma-ray bursts–Clusters of galaxies–Warm-hot intergalactic medium–Chemical evolutionExperimental Astronomy 04/2012; · 1.82 Impact Factor -
Article: EChO - Exoplanet Characterisation Observatory
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ABSTRACT: A dedicated mission to investigate exoplanetary atmospheres represents a major milestone in our quest to understand our place in the universe by placing our Solar System in context and by addressing the suitability of planets for the presence of life. EChO -the Exoplanet Characterisation Observatory- is a mission concept specifically geared for this purpose. EChO will provide simultaneous, multi-wavelength spectroscopic observations on a stable platform that will allow very long exposures. EChO will build on observations by Hubble, Spitzer and groundbased telescopes, which discovered the first molecules and atoms in exoplanetary atmospheres. EChO will simultaneously observe a broad enough spectral region -from the visible to the mid-IR- to constrain from one single spectrum the temperature structure of the atmosphere and the abundances of the major molecular species. The spectral range and resolution are tailored to separate bands belonging to up to 30 molecules to retrieve the composition and temperature structure of planetary atmospheres. The target list for EChO includes planets ranging from Jupiter-sized with equilibrium temperatures Teq up to 2000 K, to those of a few Earth masses, with Teq ~300 K. We have baselined a dispersive spectrograph design covering continuously the 0.4-16 micron spectral range in 6 channels (1 in the VIS, 5 in the IR), which allows the spectral resolution to be adapted from several tens to several hundreds, depending on the target brightness. The instrument will be mounted behind a 1.5 m class telescope, passively cooled to 50 K, with the instrument structure and optics passively cooled to ~45 K. EChO will be placed in a grand halo orbit around L2. We have also undertaken a first-order cost and development plan analysis and find that EChO is easily compatible with the ESA M-class mission framework.12/2011; -
Article: Chandra Evidence for Extended X-ray Structure in RY Tau
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ABSTRACT: We report results of a sensitive Chandra ACIS-S observation of the classical T Tauri star RY Tau. Previous studies have shown that it drives a spectacular bipolar jet whose blueshifted component is traced optically along P.A. approximately 295 degrees at separations of 1.5 - 31 arcseconds from the star. Complex X-ray emission is revealed, including a very soft non-variable spectral component (some of which may originate in shocks), a superhot flaring component (T >= 100 MK), and faint extended structure near the star. The structure is visible in deconvolved images and extends northwestward out to a separation of 1.7 arcseconds, overlapping the inner part of the optical jet. Image analysis suggests that most of the extension is real, but some contamination by PSF-induced structure within the central arcsecond may be present. The predicted temperature for a shock-heated jet based on jet speed and shock speed estimates from optical measurements is too low to explain the extended X-ray structure. Either higher speed material within the jet has escaped optical detection or other mechanisms besides shock-heating are involved. Alternative mechanisms that could produce higher temperature plasma at small offsets to the northwest of RY Tau include magnetic heating in the jet, hot plasmoids ejected at high speeds, or X-ray emission from a putative close companion whose presence has been inferred from Hipparcos variations.05/2011; -
Article: ORIGIN: Metal Creation and Evolution from the Cosmic Dawn
[show abstract] [hide abstract]
ABSTRACT: ORIGIN is a proposal for the M3 mission call of ESA aimed at the study of metal creation from the epoch of cosmic dawn. Using high-spectral resolution in the soft X-ray band, ORIGIN will be able to identify the physical conditions of all abundant elements between C and Ni to red-shifts of z=10, and beyond. The mission will answer questions such as: When were the first metals created? How does the cosmic metal content evolve? Where do most of the metals reside in the Universe? What is the role of metals in structure formation and evolution? To reach out to the early Universe ORIGIN will use Gamma-Ray Bursts (GRBs) to study their local environments in their host galaxies. This requires the capability to slew the satellite in less than a minute to the GRB location. By studying the chemical composition and properties of clusters of galaxies we can extend the range of exploration to lower redshifts (z ~ 0.2). For this task we need a high-resolution spectral imaging instrument with a large field of view. Using the same instrument, we can also study the so far only partially detected baryons in the Warm-Hot Intergalactic Medium (WHIM). The less dense part of the WHIM will be studied using absorption lines at low redshift in the spectra for GRBs.04/2011; -
Article: The Bipolar X-Ray Jet of the Classical T Tauri Star DG Tau
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ABSTRACT: We report on new X-ray observations of the classical T Tauri star DG Tau. DG Tau drives a collimated bi-polar jet known to be a source of X-ray emission perhaps driven by internal shocks. The rather modest extinction permits study of the jet system to distances very close to the star itself. Our initial results presented here show that the spatially resolved X-ray jet has been moving and fading during the past six years. In contrast, a stationary, very soft source much closer (~ 0.15-0.2") to the star but apparently also related to the jet has brightened during the same period. We report accurate temperatures and absorption column densities toward this source, which is probably associated with the jet base or the jet collimation region.01/2011; -
Article: On the origin of [NeII] 12.81 micron emission from pre-main sequence stars: Disks, jets, and accretion
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ABSTRACT: (Abridged) We have conducted a study of [NeII] line emission based on a sample of 92 pre-main sequence stars mostly belonging to the infrared Class II, including 13 accreting transition disk objects and 14 objects driving jets and outflows. We find several significant correlations between L[NeII] and stellar parameters, in particular LX and the wind mass loss rate, dM/dt. Most correlations are, however, strongly dominated by systematic scatter. While there is a positive correlation between L[NeII] and LX, the stellar mass accretion rate, dMacc/dt, induces a correlation only if we combine the largely different subsets of jet sources and stars without jets. Our results suggest that L[NeII] is bi-modally distributed, with separate distributions for the two subsamples. The jet sources show systematically higher L[NeII], by 1-2 orders of magnitude with respect to objects without jets. Jet-driving stars also tend to show higher mass accretion rates. We therefore hypothesize that the trend with dMacc/dt reflects a trend with dM/dt that is more physically relevant for [NeII] emission. L[NeII] measured for objects without known outflows and jets is found to agree with simplified calculations of [NeII] emission from disk surface layers if the measured stellar X-rays are responsible for heating and ionizing of the gas. The large scatter in L[NeII] may be introduced by variations of disk properties and the irradiation spectrum, as previously suggested. The systematically enhanced [NeII] flux from jet sources clearly suggests a role for the jets themselves, as previously demonstrated by a spatially resolved observation of the outflow system in the T Tau triple. Comment: accepted for Astronomy & Astrophysics, 25 pages, 11 figures - revisions: affiliation added, NeII flux unit in Table 3 corrected06/2010; -
Article: The disk-bearing young star IM Lup
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ABSTRACT: Classical T Tauri stars (CTTS) differ in their X-ray signatures from older pre-main sequence stars, e.g. weak-lined TTS (WTTS). CTTS show a soft excess and deviations from the low-density coronal limit in the He-like triplets. We test whether these features correlate with accretion or the presence of a disk by observing IM Lup, a disk-bearing object apparently in transition between CTTS and WTTS without obvious accretion. We analyse a Chandra grating spectrum and additional XMM-Newton data of IM Lup and accompanying optical spectra, some of them taken simultaneously to the X-ray observations. We fit the X-ray emission lines and decompose the Ha emission line in different components. In X-rays IM Lup has a bright and hot active corona, where elements of low first-ionisation potential are depleted. The He-like Ne IX triplet is in the low-density state, but due to the small number of counts a high-density scenario cannot be excluded on the 90% confidence level. In all X-ray properties IM Lup resembles a main-sequence star, but it is also compatible with CTTS signatures on the 90% confidence level, thus we cannot decide if the soft excess and deviations from the low-density coronal limit in the He-like triplets in CTTS require accretion or only the presence of a disk. IM Lup is chromospherically active, which explains most of the emission in Ha. Despite its low equivalent width, the complexity of the Ha line profile is reminiscent of CTTS. We present an estimate for the mass accretion rate of 10e-11 Msun/yr. Comment: 10 pages, 6 figures, accepted by A&A05/2010; -
Article: The large-scale disk fraction of brown dwarfs in the Taurus cloud as measured with Spitzer
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ABSTRACT: Aims. The brown dwarf (BD) formation process has not yet been completely understood. To shed more light on the differences and similarities between star and BD formation processes, we study and compare the disk fraction among both kinds of objects over a large angular region in the Taurus cloud. In addition, we examine the spatial distribution of stars and BD relative to the underlying molecular gas Methods. In this paper, we present new and updated photometry data from the Infrared Array Camera (IRAC) aboard the Spitzer Space Telescope on 43 BDs in the Taurus cloud, and recalculate of the BD disk fraction in this region. We also useed recently available CO mm data to study the spatial distribution of stars and BDs relative to the cloud's molecular gas. Results. We find that the disk fraction among BDs in the Taurus cloud is 41 \pm 12%, a value statistically consistent with the one among TTS (58 \pm 9%). We find that BDs in transition from a state where they have a disk to a diskless state are rare, and we study one isolated example of a transitional disk with an inner radius of \approx 0.1 AU (CFHT BD Tau 12, found via its relatively small mid-IR excess compared to most members of Taurus that have disks. We find that BDs are statistically found in regions of similar molecular gas surface density to those associated with stars. Furthermore, we find that the gas column density distribution is almost identical for stellar and substellar objects with and without disks. Comment: 8 page, 6 figures, Accepted in Astronomy & Astrophysics.04/2010; -
Article: Chandra and Spitzer Imaging of the Infrared Cluster in NGC 2071
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ABSTRACT: We present results of a sensitive Chandra X-ray observation and Spitzer mid-IR observations of the infrared cluster lying north of the NGC 2071 reflection nebula in the Orion B molecular cloud. We focus on the dense cluster core known as NGC 2071-IR which contains at least nine IR sources within a 40 x 40 arcsecond region. This region shows clear signs of active star formation including powerful molecular outflows, Herbig-Haro objects, and both OH and H2O masers. We use Spitzer IRAC images to aid in X-ray source identification and to determine YSO classes using mid-IR colors. Spitzer IRAC colors show that the luminous source IRS 1 is a class I protostar. IRS 1 is believed to be driving a powerful bipolar molecular outflow and may be an embedded B-type star or its progenitor. Its X-ray spectrum reveals a fluorescent Fe emission line at 6.4 keV, arising in cold material near the protostar. The line is present even in the absence of large flares, raising questions about the nature of the ionizing mechanism responsible for producing the 6.4 keV fluorescent line. Chandra also detects X-ray sources at or near the positions of IRS 2, IRS 3, IRS 4, and IRS 6 and a variable X-ray source coincident with the radio source VLA 1, located just 2 arcsec north of IRS 1. No IR data are yet available to determine a YSO classification for VLA 1, but its high X-ray absorption shows that it is even more deeply-embedded than IRS 1, suggesting that it could be an even younger, less-evolved protostar. Comment: To appear in ApJ; 30 pages, 12 figures, 3 tables06/2009; -
Article: An outflow origin of the [NeII] emission in the T Tau triplet
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ABSTRACT: (Note: this is a shortened version of the original "structured" (A&A format) abstract.) The 12.81 micrometer [NeII] line has recently gained interest as a potential tracer of gas in the tenuous surface layers of circumstellar disks. The line has been detected using the Spitzer Space Telescope in many young stars, yet these observations neiter spatially nor spectrally resolve the [NeII emission, leaving the nature of the emission mechanism unclear. Both an origin in an X-ray irradiated disk surface and an origin in strong, dissociative shocks have been proposed. We have performed a high spatial and spectral resolution (0.4 arcsec, R=30000) study of the T Tau triplet. This system contains three young stars with disks, at least one strong X-ray source (T Tau N), and diffuse regions of shocked gas surrounding the system on a scale of a few arcseconds. We find that the dominant component of [NeII] emission is centered on T Tau S and has a spatial extent of approximately 1.1 arcseconds, which is much larger than the disks in T Tau S. We detect spatially extended red-shifted emission NW of the system and fainter blue-shifted emission to the SE, which we associate with the N-S outflow from T Tau S. Only a small fraction of the [NeII] emission appears to be directly related to the X-ray bright northern component. We propose [NeII] emission in jets as a major factor causing the observed large scatter in the X-ray luminosity vs. [NeII] luminosity relation. We argue that T Tau S is the driving source of the T Tau "NW-blob" Comment: 8 pages, 6 figures, accepted for publication in Astronomy and Astrophysics02/2009; -
Article: A Survey of X-ray Emission from Wolf-Rayet Stars
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ABSTRACT: Previous X-ray studies of Wolf-Rayet (WR) stars have focused mainly on WR binary systems whose luminous high-temperature X-ray emission is thought to originate (at least partially) in colliding wind shocks between the two stars. Much less is known about the X-ray emission of putatively single WR stars, for which evidence of binarity is lacking. We present new results from an ongoing X-ray survey of single WR stars conducted with Chandra and XMM-Newton. Our objectives are to quantify the X-ray properties of single WRs and identify plausible emission mechanisms. Specifically, we would like to know if single WR stars emit predominantly soft X-rays (kT < 1 keV), as occurs in some O-type stars and is predicted for radiative wind shocks formed by the line-driven instability (LDI) mechanism. Observations to date have failed to detect any X-ray emission from single carbon-rich WC stars. In contrast, some nitrogen-rich WN stars have been detected. Recent Chandra observations of both WR 2 (WN2) and WR 134 (WN6) reveal luminous X-ray emission (log Lx 32. erg/s) comparable to that of some WR + OB binaries, including a hot plasma component (kT >> 1 keV). The presence of high-temperature plasma is not in agreement with the cool plasma expected for radiative wind shocks. Either these X-ray luminous WN stars harbor unseen companions or an alternative to the conventional LDI radiative wind shock model will be needed. This research was supported by NASA grants GO8-9008X (SAO) and NNG05GA10G (GSFC).12/2008; 41:470. -
Article: The Taurus Spitzer Legacy Project
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ABSTRACT: Without massive stars and dense stellar clusters, Taurus plays host to a distributed mode of low-mass star formation particularly amenable to observational and theoretical study. In 2005-2007, our team mapped the central 43 square degrees of the main Taurus clouds at wavelengths from 3.6 - 160 microns with the IRAC and MIPS cameras on the Spitzer Space Telescope. Together, these images form the largest contiguous Spitzer map of a single star-forming region (and any region outside the galactic plane). Our Legacy team has generated re-reduced mosaic images and source catalogs, available to the community via the Spitzer Science Center website http://ssc.spitzer.caltech.edu/legacy/all.html . This Spitzer survey is a central and crucial part of a multiwavelength study of the Taurus cloud complex that we have performed using XMM, CFHT, and the SDSS. The seven photometry data points from Spitzer allow us to characterize the circumstellar environment of each object, and, in conjunction with optical and NIR photometry, construct a complete luminosity function for the cloud members that will place constraints on the initial mass function. We present results drawing upon our catalog of several hundred thousand IRAC and thousands of MIPS sources. Initial results from our study of the Taurus clouds include new disks around brown dwarfs, new low luminosity YSO candidates, and new Herbig-Haro objects.12/2008; 41:314. -
Article: Discovery of a bipolar X-ray jet from the T Tauri star DG Tau
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ABSTRACT: We have obtained and analyzed Chandra ACIS-S observations of the strongly accreting classical T Tauri star DG Tau. Our principal goals are to map the immediate environment of the star to characterize possible extended X-rays formed in the jet, and to re-visit the anomalous, doubly absorbed X-ray spectrum of DG Tau itself. We combine our new ACIS-S data with a data set previously obtained. The data are superimposed to obtain flux and hardness images. Separate X-ray spectra are extracted for DG Tau and areas outside its point spread function. We detect a prominent X-ray jet at a position angle of PA ~225 deg (tentatively suggested by Guedel et al. 2005), coincident with the optical jet axis. We also identify a counter jet at PA = 45 deg. The X-ray jets are detected out to a distance of ~5" from the star, their sources being extended at the ACIS-S resolution. The jet spectra are soft, with a best-fit electron temperature of 3.4 MK. We find evidence for excess absorption of the counter jet. The spectrum of the DG Tau point source shows two components with largely different temperatures and absorption column densities. The similar temperatures and small absorbing gas columns of the jet sources and the soft component of the "stellar" source suggest that these sources are related, produced either by shocks or by magnetic heating in the jets. Cooling estimates suggest that the pressure in the hot gas contributes to jet expansion. The hard "stellar" component, on the other hand, is associated with a stellar corona or magnetosphere. The excessive photoelectric absorption of this component suggests the presence of dust-depleted accretion streams above coronal magnetic fields. Comment: accepted by Astronomy & Astrophysics, 11 pages, 6 figures12/2007; -
Article: The Taurus Spitzer Legacy Survey: Taking the Bull by the Horns
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ABSTRACT: One of the star-forming clouds nearest to our Sun is located 140 pc away in Taurus. Lacking dense young stellar clusters and luminous OB stars, the Taurus dark cloud hosts a distributed mode of star formation that has proved particularly amenable to observational and theoretical study. Our team used the Spitzer Space Telescope to image 43 square degrees of the main Taurus molecular cloud in order to take a deep census of young stars and disks to below the deuterium burning limit. Achieving sensitivities 20 times better than ISOCAM at 8 microns and 200 times better than IRAS at 24 microns, these observations help to characterize the lowest luminosity members of the young stellar population: collapsing protostars, young substellar objects, and edge-on disks. In addition, Spitzer's great sensitivity detects many asteroids and reveals a wealth of extragalactic sources beyond these nearby clouds. Our Legacy team has released to the community re-reduced mosaics and source catalogs for the original 29.5 square degrees which include more than 500,000 sources. An additional 14 square degrees observed in 2007 will be released in early 2008. This survey is a central and crucial part of a collaborative multiwavelength study of the Taurus cloud complex that includes data from the recent XMM, CFHT, and SDSS Taurus surveys. The 3.6 - 160 micron photometry obtained from Spitzer allow us to characterize the circumstellar environment of each object, and, in conjunction with optical and NIR photometry, construct a complete luminosity function for the cloud members that will place constraints on the initial mass function.11/2007; 39:780. -
Article: Spitzer Observations of the Taurus Molecular Cloud: Old and New YSOs
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ABSTRACT: Taurus hosts a distributed mode of low-mass star formation that has proven particularly amenable to observational and theoretical study. In 2005-7, our team mapped the central 44 square degrees of the main Taurus cloud using the IRAC and MIPS cameras on the Spitzer Space Telescope. These images form the largest contiguous Spitzer map of a single star-forming region (and any region outside the galactic plane). The Spitzer survey is a central and crucial part of a multiwavelength study of the Taurus cloud complex that we have performed using XMM, CFHT, and the Sloan Digital Sky Survey. The photometry data points from Spitzer allow us to characterize the circumstellar environment of each object. In conjunction with the rest of the surveys (in the regions where all surveys overlap), we can construct spectral energy distributions (in the best cases) from 0.212 to 160 microns for the known population. By comparison to the color distributions of the known Taurus members, we can look for new members among the rest of the detected objects. In this contribution, we will present early results for the full SEDs and colors of known members, and a first look at our new candidate members.11/2007; 39:751. -
Article: After IRAS: Revisiting the Brightest Far-Infrared Sources in Taurus with the Spitzer Taurus Survey
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ABSTRACT: The IRAS satellite provided the first uniform survey of embedded young stars in the Taurus star-forming region. To better characterize the embedded population we present data for the brightest far-infrared objects from the 43 square degree Spitzer Taurus Survey, comprising a sample of sixty-five sources brighter than 0.57 Jy at the 70 micron wavelength. Combined with companion data from SDSS, CFHT, and the XEST Optical Monitor the wavelength coverage spans from 0.29 to 160 microns. As identified from SIMBAD the sample composition is 69% young stellar objects, 12% galaxies, 9% stars, and 9% miscellaneous objects. The sample includes all known and suggested class 0 and I objects in this region prior to Spitzer. We present spectral energy distributions and revise the classifications of several objects. The Spitzer Space Telescope is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.11/2007; 39:751.
Top co-authors
Top Journals
Institutions
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2011–2012
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Netherlands Institute for Space Research, Utrecht
Utrecht, Provincie Utrecht, Netherlands
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2010–2012
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University of Vienna
Vienna, Vienna, Austria
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2007
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Princeton University
Princeton, NJ, USA
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2000–2007
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Paul Scherrer Institut
Villigen, AG, Switzerland
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2001
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Villanova University
Norristown, PA, USA
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