VLT-ISAAC 3–5 μm spectroscopy of embedded young low-mass stars

Abstract

Aims. We study in this paper the ice composition in the envelope around intermediate-mass class I Young Stellar Objects (YSOs). Methods. We performed a spectroscopic survey toward five intermediate-mass class I YSOs located in the Southern Vela molecular cloud in the L (2.85-4.0 µm) and M (4.55-4.8 µm) bands at resolving powers λ/∆λ = 600-800 up to 10 000, using the Infrared Spectrometer and Array Camera mounted on the Very Large Telescope-ANTU. Lower mass companion objects were observed simultaneously in both bands. Results. Solid H 2 O at 3 µm is detected in all sources, including the companion objects. CO ice at 4.67 µm is detected in a few main targets and one companion object. One object (LLN 19) shows little CO ice but strong gas-phase CO ro-vibrational lines in absorption. The CO ice profiles are different from source to source. The amount of water ice and CO ice trapped in a water-rich mantle may correlate with the flux ratio at 12 and 25 µm. The abundance of H 2 O-rich CO likely correlates with that of water ice. A weak feature at 3.54 µm attributed to solid CH 3 OH and a broad feature near 4.62 µm are observed toward LLN 17, but not toward the other sources. The derived abundances of solid CH 3 OH and OCN − are ∼10 ± 2% and ∼1 ± 0.2% of the H 2 O ice abundance respectively. The H 2 O optical depths do not show an increase with envelope mass, nor do they show lower values for the companion objects compared with the main protostar. The line-of-sight CO ice abundance does not correlate with the source bolometric luminosity. Conclusions. Comparison of the solid CO profile toward LLN 17, which shows an extremely broad CO ice feature, and that of its lower mass companion at a few thousand AU, which exhibits a narrow profile, together with the detection of OCN − toward LLN 17 provide direct evidences for local thermal processing of the ice.

Activation of the 3.47 μm Band by H Atom Irradiation of Carbon Grains Covered with a Water Ice Layer at 12 K

“…They attributed the continuum underlying the 3.47 mm band (the red wing of the 3 mm water ice band) to the scattering of silicate particles with a water ice mantle. Thi et al (2006) used two Gaussians to reproduce the red wing continuum and modeled the 3.47 mm band as the sum of two Gaussians centered at 3.47 and 3.44 mm and FWHM of 0.12 and 0.48 mm, respectively. Note that the values of the parameters of the first Gaussian agree with those obtained by Brooke et al (1999), who fitted a Gaussian to the 3.47 mm band of their sample of spectra.…”

CO ice mixed with CH3OH: the answer to the non-detection of the 2152 cm−1 band?

“…>90 per cent (Skinner et al 1992; Bottinelli et al 2010). The 3.54‐μm CH 3 OH feature can also be applied to constrain the CH 3 OH ice environment (Dartois et al 1999; Pontoppidan et al 2003a; Thi et al 2006). All of these studies generally conclude that at least a fraction of the CH 3 OH ice is in a water‐poor, CH 3 OH‐rich environment.…”

Photosynthesis and Photo-Stability of Nucleic Acids in Prebiotic Extraterrestrial Environments

“…These ices are exposed to doses of ionizing radiation in the form of cosmic rays and high-energy photons that can create ions and radicals in the ices that can ultimately react to form more complex molecules (Figure 2). Evidence that interstellar ices are truly processed by ionizing radiation in this manner comes from the observation of a broad absorption feature near 4.62 µm (2165 cm −1 ) in the infrared spectra of the ices in many clouds (Lacy et al 1984(Lacy et al , 1998d'Hendecourt et al 1996;Whittet et al 1996;Gibb et al 2000;Thi et al 2006). This feature is reliably reproduced in virtually all laboratory experiments involving the irradiation of ices containing sources of O, C, N, and H and is due to the C≡N stretching mode in what is most likely OCN − (Schutte and Greenberg 1997;Demyk et al 1998;van Broekhuizen et al 2004).…”

“…HC 3 N is abundant in comets (Lis et al 1997;Biver et al 2011;Dello Russo et al 2011), circumstellar disks Snyder 1982, 1984;Huang et al 2005;Pardo et al 2005), as well as in the atmosphere of Titan (Kunde et al 1981;Coustenis et al 1991;Bénilan et al 1996;Khanna 2005), the largest satellite of Saturn, known to house a very complex chemistry that may be in some points similar to what existed on the primitive Earth several billions of years ago (Chang et al 1979;Capone et al 1981;Gupta et al 1981;Raulin et al 1998;Vuitton et al 2012). OCN − has been observed in the solid phase (ice) in several astrophysical sources (Lacy et al 1984(Lacy et al , 1998d'Hendecourt et al 1996;Whittet et al 1996;Gibb et al 2000;Thi et al 2006), and is often considered to be the proof that photo-induced chemical reactions do occur at the surface of icy cold grains, since it can be formed from the irradiation of H 2 O, CO, CO 2 , and NH 3 (Schutte and Greenberg 1997;Demyk et al 1998). However, to date, OCN − has not yet been observed in the gas phase.…”