Browsing by Subject "class-i protostars"

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Far-Infrared Observations Of The Very Low Luminosity Embedded Source L1521F-IRS In The Taurus Star-Forming Region
(2009-05) Terebey, Susan; Fich, Michael; Noriega-Crespo, Alberto; Padgett, Deborah L.; Fukagawa, Misato; Audard, Marc; Brooke, Tyler; Carey, Sean; Evans, Neal J.; Guedel, Manuel; Hines, Dean; Huard, Tracy; Knapp, Gillian R.; McCabe, Caer-Eve; Menard, Francois; Monin, Jean-Louis; Rebull, Luisa; Evans, Neal J.
We investigate the environment of the very low luminosity object L1521F-IRS using data from the Taurus Spitzer Legacy Survey. The MIPS 160 mu m image shows both extended emission from the Taurus cloud and emission from multiple cold cores over a 1 degrees x 2 degrees region. Analysis shows that the cloud dust temperature is 14.2 +/- 0.4 K and the extinction ratio is A(160)/A(K) = 0.010 +/- 0.001 up to A(V) similar to 4 mag. We find kappa(160) = 0.23 +/- 0.046 cm(2) g(-1) for the specific opacity of the gas-dust mixture. Therefore, for dust in the Taurus cloud we find that the 160 mu m opacity is significantly higher than that measured for the diffuse interstellar medium, but not too different from dense cores, even at modest extinction values. Furthermore, the 160 mu m image shows features that do not appear in the IRAS 100 mu m image. We identify six regions as cold cores, i.e., colder than 14.2 K, all of which have counterparts in extinction maps or C(18)O maps. Three of the six cores contain embedded young stellar objects, which demonstrates the cores are sites of current star formation. We compare the effects of L1521F-IRS on its natal core and find there is no evidence for dust heating at 160 or 100 mu m by the embedded source. From the infrared luminosity L(TIR) = 0.024 L(circle dot) we find L(bol_int) = 0.034 -0.046 L(circle dot), thus confirming the source's low luminosity. Comparison of L1521F-IRS with theoretical simulations for the very early phases of star formation appears to rule out the first core collapse phase. The evolutionary Stateappears similar to or younger than the class 0 phase, and the estimated mass is likely to be substellar.
Identifying the Low-Luminosity Population of Embedded Protostars in the c2d Observations of Clouds and Cores
(2008-11) Dunham, Miranda M.; Crapsi, Antonio; Evans, Neal J., II; Bourke, Tyler L.; Huard, Tracy L.; Myers, Philip C.; Kauffmann, Jens; Dunham, Miranda M.; Crapsi, Antonio; Evans, Neal J., II
We present the results of a search for all embedded protostars with internal luminosities <= 1.0 L(circle dot) in the full sample of nearby, low-mass star-forming regions surveyed by the Spitzer Space Telescope Legacy Project "From Molecular Cores to Planet Forming Disks'' (c2d). The internal luminosity of a source, L(int), is the luminosity of the central source and excludes luminosity arising from external heating. On average, the Spitzer c2d data are sensitive to embedded protostars with L(int) >= 4 x 10(-3)(d/140 pc)(2) L(circle dot), a factor of 25 better than the sensitivity of the Infrared Astronomical Satellite (IRAS) to such objects. We present a set of selection criteria used to identify candidates from the Spitzer data and examine complementary data to decide whether each candidate is truly an embedded protostar. We find a tight correlation between the 70 mu m flux and internal luminosity of a protostar, an empirical result based on both observations and detailed two-dimensional radiative transfer models of protostars. We identify 50 embedded protostars with L(int) <= 1: 0 L(circle dot); 15 have L(int) <= 0: 1 L(circle dot). The intrinsic distribution of source luminosities increases to lower luminosities. While we find sources down to the above sensitivity limit, indicating that the distribution may extend to luminosities lower than probed by these observations, we are able to rule out a continued rise in the distribution below L(int) = 0.1 L(circle dot). Between 75% and 85% of cores classified as starless prior to being observed by Spitzer remain starless to our luminosity sensitivity; the remaining 15%-25% harbor low-luminosity, embedded protostars. We compile complete spectral energy distributions for all 50 objects and calculate standard evolutionary signatures (L(bol), T(bol), and L(bol)/L(smm)) and argue that these objects are inconsistent with the simplest picture of star Formation, wherein mass accretes from the core onto the protostar at a constant rate.
The Spitzer c2d Survey Of Nearby Dense Cores. XI. Infrared And Submillimeter Observations Of CB130
(2011-03) Kim, Hyo Jeong; Evans, Neal J.; Dunham, Michael M.; Chen, Jo-Hsin; Lee, Jeong-Eun; Bourke, Tyler L.; Huard, Tracy L.; Shirley, Yancy L.; De Vries, Christopher; Kim, Hyo Jeong; Evans, Neal J.; Dunham, Michael M.; Chen, Jo-Hsin
We present new observations of the CB130 region composed of three separate cores. Using the Spitzer Space Telescope, we detected a Class 0 and a Class II object in one of these, CB130-1. The observed photometric data from Spitzer and ground-based telescopes are used to establish the physical parameters of the Class 0 object. Spectral energy distribution fitting with a radiative transfer model shows that the luminosity of the Class 0 object is 0.14-0.16 L-circle dot, which is low for a protostellar object. In order to constrain the chemical characteristics of the core having the low-luminosity object, we compare our molecular line observations to models of lines including abundance variations. We tested both ad hoc step function abundance models and a series of self-consistent chemical evolution models. In the chemical evolution models, we consider a continuous accretion model and an episodic accretion model to explore how variable luminosity affects the chemistry. The step function abundance models can match observed lines reasonably well. The best-fitting chemical evolution model requires episodic accretion and the formation of CO2 ice from CO ice during the low-luminosity periods. This process removes C from the gas phase, providing a much improved fit to the observed gas-phase molecular lines and the CO2 ice absorption feature. Based on the chemical model result, the low luminosity of CB130-1 is explained better as a quiescent stage between episodic accretion bursts rather than being at the first hydrostatic core stage.