Browsing by Subject "stars: pre-main"

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Disentangling the Environment of the FU Orionis Candidate HBC 722 with Herschel
(2011-04) Green, Joel D.; Evans, Neal J., II; Kospal, Agnes; van Kempen, Tim A.; Herczeg, Gregory; Quanz, Sascha P.; Henning, Thomas; Lee, Jeong-Eun; Dunham, Michael M.; Meeus, Gwendolyn; Bouwman, Jeroen; van Dishoeck, Ewine; Chen, Jo-Hsin; Guedel, Manuel; Skinner, Stephen L.; Merello, Manuel; Pooley, David; Rebull, Luisa M.; Guieu, Sylvain; Green, Joel D.; Evans, Neal J., II
We analyze the submillimeter emission surrounding the new FU Orionis-type object, HBC 722. We present the first epoch of observations of the active environs of HBC 722, with imaging and spectroscopy from PACS, SPIRE, and HIFI on board the Herschel Space Observatory, as well as CO J = 2-1 and 350 mu m imaging (SHARC-II) with the Caltech Submillimeter Observatory. The primary source of submillimeter continuum emission in the region-2MASS 20581767+4353310-is located 16 '' south-southeast of the optical flaring source while the optical and near-infrared emission is dominated by HBC 722. A bipolar outflow extends over HBC 722; the most likely driver is the submillimeter source. We detect warm (100 K) and hot (246 K) CO emission in the surrounding region, evidence of outflow-driven heating in the vicinity. The region around HBC 722 itself shows little evidence of heating driven by the new outbursting source itself.
First Results Of The Herschel Key Program >Dust, Ice And Gas In Time> (DIGIT): Dust And Gas Spectroscopy Of HD 100546
(2010) Sturm, B.; Bouwman, J.; Henning, T.; Evans, N. J.; Acke, B.; Mulders, G. D.; Waters, Lbfm; van Dishoeck, E. F.; Meeus, G.; Green, J. D.; Augereau, J. C.; Olofsson, J.; Salyk, C.; Najita, J.; Herczeg, G. J.; van Kempen, T. A.; Kristensen, L. E.; Dominik, C.; Carr, J. S.; Waelkens, C.; Bergin, E.; Blake, G. A.; Brown, J. M.; Chen, J. H.; Cieza, L.; Dunham, M. M.; Glassgold, A.; Gudel, M.; Harvey, P. M.; Hogerheijde, M. R.; Jaffe, D.; Jorgensen, J. K.; Kim, H. J.; Knez, C.; Lacy, J. H.; Lee, J. E.; Maret, S.; Meijerink, R.; Merin, B.; Mundy, L.; Pontoppidan, K. M.; Visser, R.; Yildiz, U. A.; Evans, Neal J.; C. Salyk; Chen, J. H.; Dunham, M. M.; Harvey, P. M.; Jaffe, D.; Kim, H. J.; Lacy, J. H.
Context. We present far-infrared spectroscopic observations, taken with the Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory, of the protoplanetary disk around the pre-main-sequence star HD 100546. These observations are the first within the DIGIT Herschel key program, which aims to follow the evolution of dust, ice, and gas from young stellar objects still embedded in their parental molecular cloud core, through the final pre-main-sequence phases when the circumstellar disks are dissipated. Aims. Our aim is to improve the constraints on temperature and chemical composition of the crystalline olivines in the disk of HD 100546 and to give an inventory of the gas lines present in its far-infrared spectrum. Methods. The 69 mu m feature is analyzed in terms of position and shape to derive the dust temperature and composition. Furthermore, we detected 32 emission lines from five gaseous species and measured their line fluxes. Results. The 69 mu m emission comes either from dust grains with similar to 70 K at radii larger than 50 AU, as suggested by blackbody fitting, or it arises from similar to 200K dust at similar to 13AU, close to the midplane, as supported by radiative transfer models. We also conclude that the forsterite crystals have few defects and contain at most a few percent iron by mass. Forbidden line emission from [C II] at 157 mu m and [OI] at 63 and 145 mu m, most likely due to photodissociation by stellar photons, is detected. Furthermore, five H(2)O and several OH lines are detected. We also found high-J rotational transition lines of CO, with rotational temperatures of similar to 300K for the transitions up to J = 22-21 and T similar to 800 K for higher transitions.
The Mass-Radius Relation Of Young Stars. I. Usco 5, An M4.5 Eclipsing Binary In Upper Scorpius Observed By K2
(2015-07) Kraus, Adam L.; Cody, Ann Marie; Covey, Kevin R.; Rizzuto, Aaron C.; Mann, Andrew W.; Ireland, Michael J.; Kraus, Adam L.; Rizzuto, Aaron C.; Mann, Andrew W.
We present the discovery that UScoCTIO 5, a known spectroscopic binary in the Upper Scorpius star-forming region (P = 34 days, M-tot sin(i) = 0.64M(circle dot)), is an eclipsing system with both primary and secondary eclipses apparent in K2 light curves obtained during Campaign 2. We have simultaneously fit the eclipse profiles from the K2 light curves and the existing RV data to demonstrate that UScoCTIO 5 consists of a pair of nearly identical M4.5 stars with M-A = 0.329 +/- 0.002 M-circle dot, R-A = 0.834 +/- 0.006 R-circle dot, M-B = 0.317 +/- 0.002 M-circle dot, and R-B = 0.810 +/- 0.006 R-circle dot. The radii are broadly consistent with pre-main-sequence ages predicted by stellar evolutionary models, but none agree to within the uncertainties. All models predict systematically incorrect masses at the 25%-50% level for the HR diagram position of these mid-M dwarfs, suggesting significant modifications to mass-dependent outcomes of star and planet formation. The form of the discrepancy for most model sets is not that they predict luminosities that are too low, but rather that they predict temperatures that are too high, suggesting that the models do not fully encompass the physics of energy transport (via convection and/or missing opacities) and/or a miscalibration of the SpT-T-eff scale. The simplest modification to the models (changing T-eff to match observations) would yield an older age for this system, in line with the recently proposed older age of Upper Scorpius (tau similar to 11 Myr).
The Spitzer c2d Survey Of Nearby Dense Cores. X. Star Formation In L673 And Cb188
(2010-12) Tsitali, Anastasia E.; Bourke, Tyler L.; Peterson, Dawn E.; Myers, Phillip C.; Dunham, Michael M.; Evans, Neal J.; Huard, Tracy L.; Dunham, Michael M.; Evans, Neal J.
L673 and CB188 are two low-mass clouds isolated from large star-forming regions that were observed as part of the Spitzer Legacy Project "From Molecular Clouds to Planet Forming disks" (c2d). We identified and characterized all the young stellar objects (YSOs) of these two regions and modeled their spectral energy distributions (SEDs) to examine whether their physical properties are consistent with values predicted from the theoretical models and with the YSO properties in the c2d survey of larger clouds. Overall, 30 YSO candidates were identified by the c2d photometric criteria, 27 in L673 and 3 in CB188. We confirm the YSO nature of 29 of them and remove a false Class III candidate in L673. We further present the discovery of two new YSO candidates, one Class 0 and another possible Class I candidate in L673, therefore bringing the total number of YSO candidates to 31. Multiple sites of star formation are present within L673, closely resembling other well-studied c2d clouds containing small groups such as B59 and L1251B, whereas CB188 seems to consist of only one isolated globule-like core. We measure a star formation efficiency (SFE) of 4.6%, which resembles the SFE of the larger c2d clouds. From the SED modeling of our YSO sample we obtain envelope masses for Class I and Flat spectrum sources of 0.01-1.0 M-circle dot. The majority of Class II YSOs show disk accretion rates from 3.3 x 10(-10) to 3 x 10(-8) M-circle dot yr(-1) and disk masses that peak at 10(-4) to 10(-3) M-circle dot. Finally, we examined the possibility of thermal fragmentation in L673 as the main star-forming process. We find that the mean density of the regions where significant YSO clustering occurs is of the order of similar to 10(5) cm(-3) using 850 mu m observations and measure a Jeans Length that is greater than the near-neighbor YSO separations by approximately a factor of 3-4. We therefore suggest that other processes, such as turbulence and shock waves, may have had a significant effect on the cloud's filamentary structure and YSO clustering.
The Spitzer Survey of Interstellar Clouds in the Gould Belt. III. A Multi-Wavelength View of Corona Australis
(2011-06) Peterson, Dawn E.; Garatti, Alessio Caratti O.; Bourke, Tyler L.; Forbrich, Jan; Gutermuth, Robert A.; Jorgensen, Jes K.; Allen, Lori E.; Patten, Brian M.; Dunham, Michael M.; Harvey, Paul M.; Merin, Bruno; Chapman, Nicholas L.; Cieza, Lucas A.; Huard, Tracy L.; Knez, Claudia; Prager, Brian; Evans, Neal J., II; Dunham, Michael M.; Harvey, Paul M.; Evans, Neal J., II
We present Spitzer Space Telescope IRAC and MIPS observations of a 0.85 deg(2) field including the Corona Australis (CrA) star-forming region. At a distance of 130 pc, CrA is one of the closest regions known to be actively forming stars, particularly within its embedded association, the Coronet. Using the Spitzer data, we identify 51 young stellar objects (YS0s) in CrA which include sources in the well-studied Coronet cluster as well as sources distributed throughout the molecular cloud. Twelve of the YSOs discussed are new candidates, one of which is located in the Coronet. Known YSOs retrieved from the literature are also added to the list, and a total of 116 candidate YSOs in CrA are compiled. Based on these YSO candidates, the star Formation rate is computed to be 12M(circle dot) Myr(-1), similar to that of the Lupus clouds. A clustering analysis was also performed, finding that the main cluster core, consisting of 68 members, is elongated (having an aspect ratio of 2.36), with a circular radius of 0.59 pc and mean surface density of 150 pc(-2). In addition, we analyze outflows and jets in CrA by means of new CO and H-2 data. We present 1 3 mm interferometric continuum observations made with the Submillimeter Array (SMA) covering R CrA, IRS 5, IRS 7, and IRAS 18595-3712 (IRAS 32). We also present multi-epoch H2 maps and detect jets and outflows, study their proper motions, and identify exciting sources. The Spitzer and ISAAC/VET observations of IRAS 32 show a bipolar precessing jet, which drives a CO(2-1) outflow detected in the SMA observations. There is also clear evidence for a parsec-scale precessing outflow, which is east west oriented and originates in the SMA 2 region and likely driven by SMA 2 or IRS 7A.
The Taurus Spitzer Survey: New Candidate Taurus Members Selected Using Sensitive Mid-Infrared Photometry
(2010-02) Rebull, L. M.; Padgett, D. L.; McCabe, C. E.; Hillenbrand, L. A.; Stapelfeldt, K. R.; Noriega-Crespo, A.; Carey, S. J.; Brooke, T.; Huard, T.; Terebey, S.; Audard, M.; Monin, J. L.; Fukagawa, M.; Gudel, M.; Knapp, G. R.; Menard, Francois; Allen, L. E.; Angione, J. R.; Baldovin-Saavedra, C.; Bouvier, J.; Briggs, K.; Dougados, C.; Evans, Neal J., II; Flagey, N.; Guieu, S.; Grosso, N.; Glauser, A. M.; Harvey, Paul; Hines, D.; Latter, W. B.; Skinner, S. L.; Strom, S.; Tromp, J.; Wolf, Sebastian; Evans, Neal J., II; Harvey, Paul
We report on the properties of pre-main-sequence objects in the Taurus molecular clouds as observed in seven mid-and far-infrared bands with the Spitzer Space Telescope. There are 215 previously identified members of the Taurus star-forming region in our similar to 44 deg(2) map; these members exhibit a range of Spitzer colors that we take to define young stars still surrounded by circumstellar dust (noting that similar to 20% of the bona fide Taurus members exhibit no detectable dust excesses). We looked for new objects in the survey field with similar Spitzer properties, aided by extensive optical, X-ray, and ultraviolet imaging, and found 148 new candidate members of Taurus. We have obtained follow-up spectroscopy for about half the candidate sample, thus far confirming 34 new members, three probable new members, and 10 possible new members, an increase of 15%-20% in Taurus members. Of the objects for which we have spectroscopy, seven are now confirmed extragalactic objects, and one is a background Be star. The remaining 93 candidate objects await additional analysis and/or data to be confirmed or rejected as Taurus members. Most of the new members are Class II M stars and are located along the same cloud filaments as the previously identified Taurus members. Among non-members with Spitzer colors similar to young, dusty stars are evolved Be stars, planetary nebulae, carbon stars, galaxies, and active galactic nuclei.