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Skinner S.L.,University of Colorado at Boulder | Rebull L.,Spitzer Science Center Caltech | Gudel M.,University of Vienna
Astronomical Journal | Year: 2014

The nearby Lynds 1228 (L1228) dark cloud at a distance of 200 pc is known to harbor several young stars including the driving sources of the giant HH 199 and HH 200 Herbig-Haro (HH) outflows. L1228 has previously been studied at optical, infrared, and radio wavelengths but not in X-rays. We present results of a sensitive 37 ks Chandra ACIS-I X-ray observation of the L1228 core region. Chandra detected 60 X-ray sources, most of which are faint (<40 counts) and non-variable. Infrared counterparts were identified for 53 of the 60 X-ray sources using archival data from the Two Micron All-Sky Survey, the Spitzer Space Telescope, and the Wide-field Infrared Survey Explorer. Object classes were assigned using mid-IR colors for those objects with complete photometry, most of which were found to have colors consistent with extragalactic background sources. Seven young stellar object candidates were identified including the class I protostar HH 200-IRS which was detected as a faint hard X-ray source. No X-ray emission was detected from the luminous protostar HH 199-IRS. We summarize the X-ray and infrared properties of the detected sources and provide IR spectral energy distribution modeling of high-interest objects including the protostars driving the HH outflows. © 2014. The American Astronomical Society. All rights reserved..

Xiao H.Y.,Cornell University | Covey K.R.,Cornell University | Rebull L.,Spitzer Science Center Caltech | Charbonneau D.,Harvard University | And 4 more authors.
Astrophysical Journal, Supplement Series | Year: 2012

We analyze light curves obtained by the Trans-atlantic Exoplanet Survey (TrES) for a field centered on the L1495 dark cloud in Taurus. The Spitzer Taurus Legacy Survey catalog identifies 179 bona fide Taurus members within the TrES field; 48 of the known Taurus members are detected by TrES, as well as 26 candidate members identified by the Spitzer Legacy team. We quantify the variability of each star in our sample using the ratio of the standard deviation of the original light curve (σ orig.) to the standard deviation of a light curve that has been smoothed by 9 or 1001 epochs (σ 9 and σ 1001, respectively). Known Taurus members typically demonstrate (σ orig./σ 9) < 2.0, and (σ orig./σ 1001) < 5, while field stars reveal (σ orig./σ 9) ∼3.0 and (σ orig./σ 1001) ∼10, as expected for light curves dominated by unstructured white noise. Of the 74 Taurus members/candidates with TrES light curves, we detect significant variability in 49 sources. Adapting a quantitative metric originally developed to assess the reliability of transit detections, we measure the amount of red and white noise in each light curve and identify 18 known or candidate Taurus members with highly significant period measurements. These appear to be the first periods measured for four of these sources (HD 282276, CX Tau, FP Tau, TrES J042423+265008), and in two other cases, the first non-aliased periods (LkCa 21 and DK Tau AB). For the remainder, the TrES measurements typically agree very well (δP < 1%) with previously reported values. Including periods measured at lower confidence for 15 additional sources, we report periods for 11 objects where no previous periods were found, including 8 confirmed Taurus members. We also identify 10 of the 26 candidate Taurus members that demonstrate variability levels consistent with being bona fide TTauri stars. A Kolomgorov-Smirnov (K-S) test confirms that these new periods confirm the distinction between the rotation period distributions of stars with and without circumstellar disks, with only a 10% probability of the two populations sharing the same parent period distribution. K-S tests do suggest, however, that the updated Taurus period distribution now more closely resembles those measured in other young star-forming clusters (i.e., NGC2264, NGC6530, and the ONC). This improved agreement may reflect the exclusion of long rotation periods which are detected in Taurus at lower significance, and which may be beyond the limits of detectability in more distant star-forming regions. © 2012. The American Astronomical Society. All rights reserved.

Wolff S.C.,NOAO | Strom S.E.,NOAO | Rebull L.M.,Spitzer Science Center Caltech
Astrophysical Journal | Year: 2011

We report the results of a study of the intermediate-and high-mass stars in the young, rich star-forming complex IC 1805, based on a combination of optical, near-infrared, and mid-infrared photometry, and classification spectra. These data provide the basis for characterizing the masses and ages for stars more massive than ∼2 M⊙ and enable a study of the frequency and character of circumstellar disks associated with intermediate-and high-mass stars. Optically thick accretion disks among stars with masses 2 < M/M ⊙ < 4 are rare (∼2% of members) and absent among more massive stars. A larger fraction (∼10%) of stars with masses 2 < M/M ⊙ < 4 appear to be surrounded by disks that have evolved from the initial optically thick accretion phase. We identify four classes of such disks. These classes are based on spectral energy distributions (SEDs) of excess emission above photospheric levels: disks that are (1) optically thin based on the magnitude of the observed excess emission from 2 to 24 μm, (2) optically thin in their inner regions (r < 20 AU) and optically thick in their outer regions, (3) exhibit empty inner regions (r < 10 AU) and optically thin emission in their outer regions, and (4) exhibit empty inner regions and optically thick outer regions. We discuss, and assess the merits and liabilities of, proposed explanations for disks exhibiting these SED types and suggest additional observations that would test these proposals. © 2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A.

Van Dyk S.D.,Spitzer Science Center Caltech | Zheng W.,University of California at Berkeley | Clubb K.I.,University of California at Berkeley | Filippenko A.V.,University of California at Berkeley | And 7 more authors.
Astrophysical Journal Letters | Year: 2013

We conducted Hubble Space Telescope (HST) Snapshot observations of the Type IIb supernova (SN) 2011dh in M51 at an age of 641 days with the Wide Field Camera 3. We find that the yellow supergiant star, clearly detected in pre-SN HST images, has disappeared, implying that this star was almost certainly the progenitor of the SN. Interpretation of the early time SN data which led to the inference of a compact nature for the progenitor, and to the expected survival of this yellow supergiant, is now clearly incorrect. We also present ground-based UBVRI light curves obtained with the Katzman Automatic Imaging Telescope at Lick Observatory up to SN age 70 days. From the light-curve shape including the very late time HST data, and from recent interacting binary models for SN 2011dh, we estimate that a putative surviving companion star to the now deceased yellow supergiant could be detectable by late 2013, especially in the ultraviolet. No obvious light echoes are detectable yet in the SN environment. © 2013. The American Astronomical Society. All rights reserved.

Van Dyk S.D.,Spitzer Science Center Caltech
Astronomical Journal | Year: 2013

Type IIn supernovae (SNe IIn) have been found to be associated with significant amounts of dust. These core-collapse events are generally expected to be the final stage in the evolution of highly massive stars, either while in an extreme red supergiant phase or during a luminous blue variable phase. Both evolutionary scenarios involve substantial pre-supernova mass loss. I have analyzed the SN IIn 1995N in MCG -02-38-017 (Arp 261), for which mid-infrared archival data obtained with the Spitzer Space Telescope in 2009 (∼14.7 yr after explosion) and with the Wide-field Infrared Survey Explorer in 2010 (∼15.6-16.0 yr after explosion) reveal a luminous (∼2 × 10 7 L ⊙) source detected from 3.4 to 24 μm. These observations probe the circumstellar material, set up by pre-SN mass loss, around the progenitor star and indicate the presence of ∼0.05-0.12 M ⊙ of pre-existing, cool dust at ∼240 K. This is at least a factor ∼10 lower than the dust mass required to be produced from SNe at high redshift, but the case of SN 1995N lends further evidence that highly massive stars could themselves be important sources of dust. © 2013. The American Astronomical Society. All rights reserved.

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