Identifying the Low-Luminosity Population of Embedded Protostars in the c2d Observations of Clouds and Cores

By M. Dunham, A. Crapsi, N. Evans II, T. Bourke, T. Huard, P. Myers, Jens Kauffmann. 2007

241 citations recorded by the source corpus.

We present the results of a search for all embedded protostars with internal luminosities ≤1.0 L☉ 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, Lint, 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 Lint ⩾ 4 × 10−3(d/140 pc)2 L☉, 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 μm 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 Lint ⩽ 1.0 L☉; 15 have Lint ⩽ 0.1 L☉. 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 Lint = 0.1 L☉. 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 (Lbol, Tbol, and Lbol/Lsmm) 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.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/352aabd6f0ea4c3948c1cdbb1d0c41fe4628a4e6

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. N. Evans II
2. K. Luhman
3. P. Myers
4. L. Hartmann
5. Ralf Klessen
6. Mark R. Krumholz
7. L. Allen
8. N. Calvet

In Instrumentation

1. N. Evans II
2. K. Luhman
3. L. Hartmann
4. Eduard I. Vorobyov
5. N. Calvet
6. G. Chabrier
7. A. Heiderman
8. P. Myers

Citations in the corpus

• EVOLUTIONARY SIGNATURES IN THE FORMATION OF LOW-MASS PROTOSTARS. II. TOWARD RECONCILING MODELS AND OBSERVATIONS (2005, background): “This sample is based primarily on the work of Enoch et al. (2009) and Dunham et al. (2008); the former compiled a complete sample of embedded objects in Perseus, Serpens, and Ophiuchus while the latter presented the results of a search for all low-luminosity (.”
• PROPERTIES OF THE YOUNGEST PROTOSTARS IN PERSEUS, SERPENS, AND OPHIUCHUS (2008, background): “The characteristics of low luminosity protostars in Perseus, Serpens, and Ophiuchus are analyzed in Dunham et al. (2008).”
• The Formation and Early Evolution of Low-Mass Stars and Brown Dwarfs (2012, background): “…samples of molecular cloud cores, often selected based on the absence of previously detected stars (“starless” cores), or searching for candidate protostars anywhere in the Spitzer images of a star-forming region regardless of the availability of previous detections of cores (Dunham et al. 2008).”
• SDC13 infrared dark clouds: longitudinally collapsing filaments? (2013, methodology): “Finally, based on the 24 µm flux of protostellar sources and an assumed extinction, one may obtain an estimate of the source bolometric luminosity (Dunham et al. 2008).”
• THE SPITZER c2d LEGACY RESULTS: STAR-FORMATION RATES AND EFFICIENCIES; EVOLUTION AND LIFETIMES (2008, methodology): “A more thorough study (Dunham et al. 2008) of the low luminosity end that dealt with these effects found 15 objects with internal luminosity, Lint ≤ 0.1 L⊙.”
• A census of dense cores in the Aquila cloud complex: SPIRE/PACS observations from the Herschel Gould Belt survey (2015, background): “Indeed, the presence of point-like 70 μm emission traces the internal luminosity of a protostar very well (e.g., Dunham et al. 2008), and Herschel/PACS observations of nearby (d < 500 pc) clouds even have the sensitivity to detect candidate “first hydrostatic cores”, the very first and…”
• YOUNG STELLAR OBJECTS IN THE GOULD BELT (2015, background): “With the sensitivity of Spitzer, Class 0 sources are easily detected in the infrared (e.g., Noriega-Crespo et al. 2004; Young et al. 2004; Jørgensen et al. 2006; Dunham et al. 2006, 2008; Tobin et al. 2010).”
• THE HERSCHEL ORION PROTOSTAR SURVEY: SPECTRAL ENERGY DISTRIBUTIONS AND FITS USING A GRID OF PROTOSTELLAR MODELS (2016, background): “The number of VeLLOs in our sample is likely larger, given that VeLLOs are defined as having internal luminosities less than 0.1 L⊙, and the bolometric luminosity has contributions from both the internal luminosity and that due to external heating (see Dunham et al. 2008).”
• EPISODIC ACCRETION AT EARLY STAGES OF EVOLUTION OF LOW-MASS STARS AND BROWN DWARFS: A SOLUTION FOR THE OBSERVED LUMINOSITY SPREAD IN H–R DIAGRAMS? (2009, background): “Current observational analysis of embedded protostars strongly suggest that accretion onto forming stars must be transient, with very large fluctuations (Dunham et al. 2008; Enoch et al. 2009; Evans et al. 2009).”
• RESOLVING THE LUMINOSITY PROBLEM IN LOW-MASS STAR FORMATION (2011, background): “…is based primarily on the association of Spitzer sources featuring rising SEDs and red colors with millimeter continuum sources (Enoch et al. 2009a; Dunham et al. 2008) and is likely biased against such objects since they would often not meet these criteria and would instead be assumed to be…”
• PROSAC: a submillimeter array survey of low-mass protostars - II. The mass evolution of envelopes, disks, and stars from the class 0 through I stages (2009, unknown): “The luminosity can either be derived from the full spectral energy distribution of each source or by using the empirical correlation between source internal luminosity and 70µm Spitzer flux by Dunham et al. (2008).”