Multiwavelength study of the high-latitude cloud L1642: chain of star formation

Abstract

Context. L1642 is one of the two high galactic latitude (|b| > 30 • ) clouds confirmed to have active star formation. Aims. We examine the properties of this cloud, especially the large-scale structure, dust properties, and compact sources at different stages of star formation.Methods. We present high-resolution far-infrared and submillimetre observations with the Herschel and AKARI satellites and millimetre observations with the AzTEC/ASTE telescope, which we combined with archive data from near-and mid-infrared (2MASS, WISE) to millimetre wavelength observations (Planck).Results. The Herschel observations, combined with other data, show a sequence of objects from a cold clump to young stellar objects (YSOs) at different evolutionary stages. Source B-3 (2MASS J04351455-1414468) appears to be a YSO forming inside the L1642 cloud, instead of a foreground brown dwarf, as previously classified. Herschel data reveal striation in the diffuse dust emission around the cloud L1642. The western region shows striation towards the NE and has a steeper column density gradient on its southern side. The densest central region has a bow-shock like structure showing compression from the west and has a filamentary tail extending towards the east. The differences suggest that these may be spatially distinct structures, aligned only in projection. We derive values of the dust emission cross-section per H nucleon of σ e (250 μm) = 0.5−1.5 × 10 −25 cm 2 /H for different regions of the cloud. Modified black-body fits to the spectral energy distribution of Herschel and Planck data give emissivity spectral index β values 1.8-2.0 for the different regions. The compact sources have lower β values and show an anticorrelation between T and β. Conclusions. Markov chain Monte Carlo calculations demonstrate the strong anticorrelation between β and T errors and the importance of millimetre wavelength Planck data in constraining the estimates. L1642 reveals a more complex structure and sequence of star formation than previously known.

Herscheland SCUBA-2 observations of dust emission in a sample ofPlanckcold clumps

“…That result is, of course, affected by larger uncertainties. One can note that also in Malinen et al (2014), the use of different wavelength ranges (from 100-500 µm to 160-1380 µm) did not result in significant changes in the (T , β) estimates of the protostellar and starless cores of the cloud LDN 1642.…”

The Hawaii Infrared Parallax Program. Ii. Young Ultracool Field Dwarfs* †

“…Our proper motion measurement of (µ α , µ δ ) = (−0.6 ± 1.9, +9.3 ± 2.0) mas/yr is consistent with that of the IRASexcess star EW Eri associated with the cloud (Sandell et al 1987), which has a proper motion of (−5.3 ± 5.6, +7.1 ± 5.5 mas/yr) from UCAC4 (Zacharias et al 2013). Allers & Liu (2013a) noted that this object's WISE photometry (3.6-22 µm) shows no sign of a disk, while Malinen et al (2014) associate this object with a source detected in far-IR, submillimeter, and millimeter data (100-1100 µm). The overall (1.2-1100 µm) spectral energy distribution points to a Class III source, namely one without a substantial circumstellar disk but still possessing residual material at large separations.…”

Galactic cold cores

“…The submillimetre dust opacity has previously been studied in relation to both dust extinction (Terebey et al 2009;Flagey et al 2009;Juvela et al 2011;Martin et al 2012;Roy et al 2013;Malinen et al 2013Malinen et al , 2014 and to HI Lagache et al 1999;Planck Collaboration XXIV 2011;Planck Collaboration XXV 2011;Martin et al 2012). Boulanger et al (1996) compared COBE observations of FIR dust emission with the hydrogen 21 cm observations.…”

“…Montillaud (2015) presented the analysis of all clumps and cores found in our Herschel fields, including a comparison with the population of young stellar objects (YSOs). Further studies concentrated especially on high latitude clouds (Malinen et al 2014;Rivera-Ingraham et al and Ristorcelli et al, in prep. ).…”