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Register a new userThe Environment and Nature of the Class I Protostar Elias 29: Molecular Gas Observations and the Location of Ices
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A.C.A. Boogert
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A (sub-)millimeter line and continuum study of the class I protostar Elias 29 in the Rho Ophiuchi molecular cloud is presented, whose goals are to understand the nature of this source, and to locate the ices that are abundantly present along this line of sight. Within 15-60 beams, several different components contribute to the line emission. Two different foreground clouds are detected, an envelope/disk system and a dense ridge of HCO+ rich material. The latter two components are spatially separated in millimeter interferometer maps. We analyze the envelope/disk system by using inside-out collapse and flared disk models. The disk is in a relatively face-on orientation (<60 degrees), which explains many of the remarkable observational features of Elias 29, such as its flat SED, its brightness in the near infrared, the extended components found in speckle interferometry observations, and its high velocity molecular outflow. It cannot account for the ices seen along the line of sight, however. A small fraction of the ices is present in a (remnant) envelope of mass 0.12-0.33 Msun, but most of the ices (~70%) are present in cool (T<40 K) quiescent foreground clouds. This explains the observed absence of thermally processed ices (crystallized H2O) toward Elias 29. Nevertheless, the temperatures could be sufficiently high to account for the low abundance of apolar (CO, N2, O2) ices. This work shows that it is crucial to obtain spectrally and spatially resolved information from single-dish and interferometric molecular gas observations in order to determine the nature of protostars and to interpret infrared ISO satellite observations of ices and silicates along a pencil beam.
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We present the study of the effects of high energy cosmic rays (CRs) over the astrophysical ices, observed toward the embedded class I protostar Elias 29, by using computational modeling and laboratory data. Its spectrum was observed with {it Infrared Space Observatory - ISO}, covering 2.3 - 190 $mu$m. The modeling employed the three-dimensional Monte Carlo radiative transfer code RADMC-3D (Dullemond et al. 2012) and laboratory data of bombarded ice grains by CRs analogs, and unprocessed ices (not bombarded). We are assuming that Elias 29 has a self-irradiated disk with inclination $i =$ 60$^{circ}$, surrounded by an envelope with bipolar cavity. The results show that absorption features toward Elias 29, are better reproduced by assuming a combination between unprocessed astrophysical ices at low temperature (H$_2$O, CO, CO$_2$) and bombarded ices (H$_2$O:CO$_2$) by high energy CRs. Evidences of the ice processing around Elias 29 can be observed by the good fitting around 5.5-8.0 $mu$m, by polar and apolar ice segregation in 15.15-15.25 $mu$m, and by presence of the CH$_4$ and HCOOH ices. Given that non-nitrogen compounds were employed in this work, we assume that absorption around 5.5-8.0 $mu$m should not be associated with NH$_4^+$ ion (Shutte & Khanna2003), but more probably with aliphatic ethers (e.g. R1-OCH$_2$-R2), CH$_3$CHO and related species. The results obtained in this paper are important, because they show that the environment around protostars is better modeled considering processed samples and, consequently, demonstrates the chemical evolution of the astrophysical ices.
[Abridged] We investigated the X-ray characteristics of the Class I YSO Elias 29 with joint XMM-Newton and NuSTAR observations of 300 ks and 450 ks, respectively. These are the first observations of a very young (<1 Myr) stellar object in a band encompassing simultaneously both soft and hard X-rays. In addition to the hot Fe complex at 6.7 keV, we observed fluorescent emission from Fe at $sim6.4$ keV, confirming the previous findings. The line at 6.4 keV is detected during quiescent and flaring states and its flux is variable. The equivalent width is found varying in the $approx 0.15--0.5$ keV range. These values make unrealistic a simple model with a centrally illuminated disk and suggest a role of the cavity containing Elias 29 and possibly reverberation processes that could occur in it. We observed two flares, with duration of 20 ks and 50 ks, respectively. We systematically observed an increase of $N_H$ during the flares of a factor five. This behavior has been observed during flares previously detected in Elias 29 with XMM-Newton and ASCA. The phenomenon hints that the flaring regions could be buried under the accretion streams and at high stellar latitudes, as the X-rays from flares pass through gas denser than the gas along the line of sight of the quiescent corona. In a different scenario, a contribution from scattered soft photons to the primary coronal emission could mimic a shallower $N_H$ in the quiescent spectrum. In the spectrum of the full NuSTAR exposure, we detect hard X-ray emission in the band $approx20-80$ keV in excess with respect to the thermal emission. The hard X-ray emission could be due to a population of energetic electrons accelerated by the magnetic field along the accretion streams. These particles could concur to pumping up the Fe fluorescence of cold Fe of the disk along with X-ray photons with $E>7.11$ keV.
We have observed the Class I protostellar source Elias 29 with Atacama Large Millimeter/submillimeter Array (ALMA). We have detected CS, SO, $^{34}$SO, SO$_2$, and SiO line emissions in a compact component concentrated near the protostar and a ridge component separated from the protostar by 4arcsec ($sim 500$ au). The former component is found to be abundant in SO and SO$_2$ but deficient in CS. The abundance ratio SO/CS is as high as $3^{+13}_{-2} times 10^2$ at the protostar, which is even higher than that in the outflow-shocked region of L1157 B1. However, organic molecules (HCOOCH$_3$, CH$_3$OCH$_3$, CCH, and c-C$_3$H$_2$) are deficient in Elias 29. We attribute the deficiency in organic molecules and richness in SO and SO$_2$ to the evolved nature of the source or the relatively high dust temperature (protectraisebox{-0.7ex}{$:stackrel{textstyle >}{sim}:$} 20 K) in the parent cloud of Elias 29. The SO and SO$_2$ emissions trace rotation around the protostar. Assuming a highly inclined configuration ($i geq 65$degr; 0degr for a face-on configuration) and Keplerian motion for simplicity, the protostellar mass is estimated to be (0.8 -- 1.0) Msun. The $^{34}$SO and SO$_2$ emissions are asymmetric in their spectra; the blue-shifted components are weaker than the red-shifted ones. Although this may be attributed to the asymmetric molecular distribution, other possibilities are also discussed.
We present observations of Taurus-Auriga Class I/II protostars obtained with the Spitzer InfraRed Spectrograph. Detailed spectral fits to the 6 and 15 micron features are made, using publicly-available laboratory data, to constrain the molecular composition, abundances, and levels of thermal processing along the lines of sight. We provide an inventory of the molecular environments observed, which have an average composition dominated by water ice with ~12% CO_2 (abundance relative to H_2O), >~2-9% CH_3OH, <~14% NH_3, ~4% CH_4, ~2% H_2CO, ~0.6% HCOOH, and ~0.5% SO_2. We find CO_2/H_2O ratios nearly equivalent to those observed in cold clouds and lines of sight toward the galactic center. The unidentified 6.8 micron profiles vary from source to source, and it is shown to be likely that even combinations of the most common candidates (NH_4+ and CH_3OH) are inadequate to explain the feature fully. We discuss correlations among SED spectral indices, abundance ratios, and thermally-processed ice fractions and their implications for CO_2 formation and evolution. Comparison of our spectral fits with cold molecular cloud sight-lines indicates abundant prestellar ice environments made even richer by the radiative effects of protostars. Our results add additional constraints and a finer level of detail to current full-scale models of protostellar and protoplanetary systems.
The Ophiuchus clouds, in particular L~1688, are an excellent region to study the embedded phases of star formation, due to the relatively large number of protostars. However, the standard method of finding and characterizing embedded young stellar objects (YSOs) through just their infrared spectral slope does not yield a reliable sample. This may affect the age determinations, often derived from the statistics on the total number of embedded YSOs and pre-main sequence stars within a cloud.Our aim is to characterize the structure of protostellar envelopes on an individual basis and to correctly identify the embedded YSO population of L1688. Spectral maps of the HCO+ J=4--3 and C18O J=3--2 lines using the HARP-B array on the James Clerk Maxwell Telescope and SCUBA 850 micron dust maps are obtained of all sources in the L1688 region with infrared spectral slopes consistent with, or close to, that of embedded YSOs. Selected 350 micron maps obtained with the Caltech Submillimeter Observatory are presented as well. The properties, extent and variation of dense gas, column density and dust on scalesup to 1 are probed at 15 resolution. Using the spatial variation of the gas and dust, together with the intensity of the HCO+ J=4--3 line, we are able to accurately identify the truly embedded YSOs and determine their properties. RESULTS The protostellar envelopes range from 0.05 to 0.5 Msun in mass. The concentration of HCO+ emission (~0.5 to 0.9) is generally higher than that of the dust concentration. Combined with absolute intensities, HCO+ proves to be a better tracer of protostellar envelopes than dust, which can contain disk and cloud contributions. Our total sample of 45 sources, including all previously classified Class I sources, several flat-spectrum sources and some known disks, was re-classified using the ....
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