The low-mass YSO CB230-A: investigating the protostar and its jet with NIR spectroscopy and Spitzer observations

Abstract

Context. To investigate the earliest phases of star formation and study how newly-born stars interact with the surrounding medium, we performed a line and continuum survey at NIR and mm-wavelengths of a sample of relatively isolated Bok globules. Aims. We present a follow-up observational program of a star-forming site in the globule CB230. From narrow-band continuum observations of this site, we had discovered a bright [FeII] jet, which originates in the low-mass YSO CB230-A. We aim to investigate the physical properties of the region from where the jet is launched. Methods. Our analysis was carried out using low-resolution NIR spectra acquired with the camera NICS at the TNG telescope, with JH and HK grisms and a 1 arcsec-wide slit. These observational data were complemented with infrared photometric data from the Spitzer space telescope archive. Results. The relevant physical properties of CB230-A were constrained by SED fitting of fluxes from the NIR to the mm. The YSO spectrum exhibits a significant number of atomic and molecular emission lines and absorption features. The characteristics of this spectrum suggest that we are observing a region in the close vicinity of CB230-A, i.e. its photosphere and/or an active accretion disk. The spectra of the knots in the jet contain a large number of emission lines, including a rich set of [FeII] lines. Emission due to H 2 and [FeII] are not spatially correlated, confirming that [FeII] and H 2 are excited by different mechanisms, in agreement with the models where [FeII] traces dissociative J-shocks and molecular hydrogen traces slower C-shocks. By using intensity ratios involving density-sensitive [FeII] lines, we estimated the electron densities along the jet to be 6 × 10 3 -1 × 10 4 cm −3 . This indicates either high density post-shock regions of ionised gas or regions with a high degree of ionisation. Conclusions. By combining the present data with previously obtained maps at NIR-and mm-wavelengths, the emerging scenario is that CB230-A is a Class 0/I YSO driving an atomic jet that is observed to be almost monopolar probably due to its inclination to the plane of the sky and the resulting higher extinction of its red side. This primary jet appears to be sufficiently energetic to open the cavity visible in the NIR images and drive the large-scale molecular outflow observed at mm-wavelengths. CB230-A was revealed to be a good location to test the innermost structure of accreting low-mass protostars.

SMA observations of polarized dust emission in solar-type Class 0 protostars: Magnetic field properties at envelope scales

“…These are separated by 10 and are aligned in the east-west direction (Launhardt 2001(Launhardt , 2004. The eastern object, IRS2, is not detected beyond 24 µm (Massi et al 2008;Launhardt et al 2013). Outflows.…”

“…The sample only contains low-mass Class 0 protostars, except for SVS13-A. The M env and L bol are from Massi et al (2008) for CB230, Launhardt et al (2013) for B335, Crimier et al (2010) for IRAS16293, Sadavoy et al (2014), Ladjelate et al (in prep. ), and Maury et al (in prep.…”

Vla and Carma Observations of Protostars in the Cepheus Clouds: Sub-Arcsecond Proto-Binaries Formed via Disk Fragmentation

“…Near-infrared imaging previously detected a companion separated from IRS1 by ∼10 (3000 AU) to the east (Yun 1996); we refer to this companion as IRS2. IRS2 has been detected at wavelengths between 1.2 µm and 24 µm (Massi et al 2008), but is undetected in Herschel data at 100 µm (Launhardt et al 2013), SCUBA at 450 µm (Launhardt et al 2010), and OVRO 1.3 mm and 3.4 mm data Launhardt 2001). CB230 IRS1 is also classified as a Class 0/I source with L submm /L bol = 0.037 and T bol = 189 K (Launhardt et al 2013).…”

Deriving the Extinction to Young Stellar Objects using [Fe II] Near-infrared Emission Lines: Prescriptions from GIANO High-resolution Spectra

“…They suggested that these facts point to inaccuracies in the theoretical transition probabilities available. Massi et al (2008) cautioned against the possibility that the discrepancy between ratios could arise from inaccuracies in the telluric absorption correction caused by the 1.257 µm line falling in the region of the 1 ∆ g absorption band of atmospheric O 2 . Giannini et al (2015a) tried determining the Einstein spontaneous emission rates of the three Fe + lines using X-shooter spectra of HH1, still finding a few cases of discrepancies between their determination and data from the literature.…”