The Herschel Orion Protostar Survey: Spectral Energy Distributions and Fits Using a Grid of Protostellar Models

Abstract

We present key results from the Herschel Orion Protostar Survey (HOPS): spectral energy distributions (SEDs) and model fits of 330 young stellar objects, predominantly protostars, in the Orion molecular clouds. This is the largest sample of protostars studied in a single, nearby star formation complex. With near-infrared photometry from 2MASS, mid-and far-infrared data from Spitzer and Herschel, and submillimeter photometry from APEX, our SEDs cover 1.2 -870 µm and sample the peak of the protostellar envelope emission at ∼ 100 µm. Using mid-IR spectral indices and bolometric temperatures, we classify our sample into 92 Class 0 protostars, 125 Class I protostars, 102 flatspectrum sources, and 11 Class II pre-main-sequence stars. We implement a simple protostellar model (including a disk in an infalling envelope with outflow cavities) to generate a grid of 30,400 model SEDs and use it to determine the best-fit model parameters for each protostar. We argue that far-IR data are essential for accurate constraints on protostellar envelope properties. We find that most protostars, and in particular the flat-spectrum sources, are well fit. The median envelope density and median inclination angle decrease from Class 0 to Class I to flat-spectrum protostars, despite the broad range in best-fit parameters in each of the three categories. We also discuss degeneracies in our model parameters. Our results confirm that the different protostellar classes generally correspond to an evolutionary sequence with a decreasing envelope infall rate, but the inclination angle also plays a role in the appearance, and thus interpretation, of the SEDs.

Slingshot mechanism in Orion: Kinematic evidence for ejection of protostars by filaments

“…Figures 6 and 7 show the gas column density as traced by dust emission in Orion A (Stutz & Kainulainen 2015) with, respectively, Class 0 and Class I protostars (Furlan et al 2016) and pre-main-sequence Class II stars (Megeath et al 2012) superposed. The pre-main-sequence stars (hereafter stars) shown Megeath et al 2012) compared to gas density as traced by dust emission (Stutz & Kainulainen 2015).…”

“…6. Positions of protostars (Furlan et al 2016) compared to gas density as traced by dust emission (Stutz & Kainulainen 2015). Protostars lie almost exclusively on the ridges of columns.…”

Stacked Average Far-infrared Spectrum of Dusty Star-forming Galaxies from the Herschel/SPIRE Fourier Transform Spectrometer∗

“…The luminosity of the protostar itself (from contraction and deuterium burning) can be ignored because the age is too young (Myers et al 1998). By contrast, infrared observations of V380 Ori NE indicate L bol =3.9 L e (Furlan et al 2016). Considering the uncertainties and assumptions involved, it is unclear whether or not the difference between the expected and observed luminosities is significant.…”

“…Finally, external heating by the interstellar radiation field can increase the flux densities in the long wavelength bands, though the effect on the spectral slope may be small. This effect may be noticeable only for low-luminosity objects (<1 L e ) in extremely strong radiation fields (Shirley et al 2002;Furlan et al 2016). Because the bolometric luminosities of HH 34 MMS, V380 Ori NE, and HH 147 MMS are L bol =18.8, 3.9, and 15.5 L e , respectively (Furlan et al 2016), it is unlikely that the external heating can affect the spectral slopes.…”

“…Later studies showed that this outflow is driven by a deeply embedded protostar (Davis et al 2000), one of the extreme Class 0 protostars reported by Stutz et al (2013). This protostar, HOPS 169, has a bolometric luminosity of L bol = 3.9 L e and bolometric temperature of T bol =33 K (Furlan et al 2016). Maps of the infrared H 2 line and CO =  J 4 3 line revealed that the V380 Ori NE outflow is a highly collimated jet flowing along a point-symmetric curve (Davis et al 2000; Stanke et al 2002).…”