The nature of the Class I population in Ophiuchus as revealed through gas and dust mapping

Bruderer

et al. 2015

A&A

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162

215

Context. Transitional disks with large dust cavities are important laboratories in which to study planet formation and disk evolution. Cold gas may still be present inside these cavities, but quantying this gas is challenging. The gas content is important for constraining the origin of the dust cavity. Aims. We use Atacama Large Millimeter/submillimeter Array (ALMA) observations of 12 CO 6-5 and 690 GHz (Band 9) continuum of five well-studied transitional disks. In addition, we analyze previously published Band 7 observations of a disk in the 12 CO 3-2 line and 345 GHz continuum. The observations are used to set constraints on the gas and dust surface density profiles, in particular, the drop δ gas of the gas density inside the dust cavity. Methods. The physical-chemical modeling code DALI was used to simultaneously analyze the gas and dust images. We modeled SR21, HD 135344B, LkCa15, SR24S, and RX J1615-3255 (Band 9) and J1604-2130 (Band 7). The spectral energy distribution and continuum visibility curve constrain the dust surface density. Then we used the same model to calculate the 12 CO emission, which we compared with the observations through spectra and intensity cuts. The amount of gas inside the cavity was quantified by varying the δ gas parameter. Results. Model fits to the dust and gas indicate that gas is still present inside the dust cavity for all disks, but at a reduced level. The gas surface density drops inside the cavity by at least a factor 10, while the dust density drops by at least a factor 1000. Disk masses are comparable with previous estimates from the literature, cavity radii are found to be smaller than in the data obtained with the 345 GHz SubMillimeter Array. Conclusions. The derived gas surface density profiles suggest that the cavity was cleared by one or more companions in all cases, which trapped the millimeter-sized dust at the edge of the cavity.

Section: Continuum and Line Mapsmentioning

confidence: 99%

Gas density drops inside dust cavities of transitional disks around young stars observed with ALMA

Marel

Bruderer

et al. 2015

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162

215

“…These sources are located in the Ophiuchus molecular cloud, where two low-density foreground sheets contribute to the lowest J 1-0 and 2-1 lines (e.g., Loren 1989;van Kempen et al 2009d). To take this into account, a single slab foreground cloud is added in front of the protostars with 15 K temperature, 1.5 × 10 4 cm −3 H 2 density, and 10 16 cm −2 CO column density.…”

Section: Co Abundance Profilesmentioning

confidence: 99%

High-JCO survey of low-mass protostars observed withHerschel-HIFI

Yıldız

Kristensen

et al. 2013

A&A

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131

Context. In the deeply embedded stage of star formation, protostars start to heat and disperse their surrounding cloud cores. The evolution of these sources has traditionally been traced through dust continuum spectral energy distributions (SEDs), but the use of CO excitation as an evolutionary probe has not yet been explored due to the lack of high-J CO observations. Aims. The aim is to constrain the physical characteristics (excitation, kinematics, column density) of the warm gas in low-mass protostellar envelopes using spectrally resolved Herschel data of CO and compare those with the colder gas traced by lower excitation lines. Methods. Herschel-HIFI observations of high-J lines of 12 CO, 13 CO, and C 18 O (up to J u = 10, E u up to 300 K) are presented toward 26 deeply embedded low-mass Class 0 and Class I young stellar objects, obtained as part of the Water In Star-forming regions with Herschel (WISH) key program. This is the first large spectrally resolved high-J CO survey conducted for these types of sources. Complementary lower J CO maps were observed using ground-based telescopes, such as the JCMT and APEX and convolved to matching beam sizes. Results. The 12 CO 10-9 line is detected for all objects and can generally be decomposed into a narrow and a broad component owing to the quiescent envelope and entrained outflow material, respectively. The 12 CO excitation temperature increases with velocity from ∼60 K up to ∼130 K. The median excitation temperatures for 12 CO, 13 CO, and C 18 O derived from single-temperature fits to the J u = 2-10 integrated intensities are ∼70 K, 48 K and 37 K, respectively, with no significant difference between Class 0 and Class I sources and no trend with M env or L bol . Thus, in contrast to the continuum SEDs, the spectral line energy distributions (SLEDs) do not show any evolution during the embedded stage. In contrast, the integrated line intensities of all CO isotopologs show a clear decrease with evolutionary stage as the envelope is dispersed. Models of the collapse and evolution of protostellar envelopes reproduce the C 18 O results well, but underproduce the 13 CO and 12 CO excitation temperatures, due to lack of UV heating and outflow components in those models. The H 2 O 1 10 − 1 01 /CO 10-9 intensity ratio does not change significantly with velocity, in contrast to the H 2 O/CO 3-2 ratio, indicating that CO 10-9 is the lowest transition for which the line wings probe the same warm shocked gas as H 2 O. Modeling of the full suite of C 18 O lines indicates an abundance profile for Class 0 sources that is consistent with a freeze-out zone below 25 K and evaporation at higher temperatures, but with some fraction of the CO transformed into other species in the cold phase. In contrast, the observations for two Class I sources in Ophiuchus are consistent with a constant high CO abundance profile. Conclusions. The velocity resolved line profiles trace the evolution from the Class 0 to the Class I phase through decreasing line intensities, less prominent outflow...

“…HH 46 is a Class I protostar famous for its well-characterized outflow, pointed to the south-west (Chernin & Masson 1991;Heathcote et al 1996;Stanke et al 1999;Noriega-Crespo et al 2004;Velusamy et al 2007). It is extensively discussed in van Kempen et al (2009a). IRAS 12496-7650, also known as DK Cha, is one of the brightest protostars in the southern hemisphere and a potential driving source of HH 54 (van Kempen et al 2006).…”

Section: Source Listmentioning

confidence: 99%

“…Jørgensen et al 2005a) coupled with a lack of some collisional rate coefficients make these species less suitable tracers for the bulk of the low-mass embedded YSOs. In practice, the column density of the surrounding cloud (and that of any unrelated foreground clouds) is best probed by low excitation optically thin transitions of molecules with a low dipole moment, such as the isotopologues of CO, e.g., C 18 O 2-1 or 3-2 (van Kempen et al 2009b). For molecular outflows the line wings of various 12 CO transitions have been efficiently used as tracers of their properties (Cabrit & Bertout 1992;Bontemps et al 1996;Hogerheijde et al 1998;Bachiller & Tafalla 1999;Hatchell et al 1999;Hatchell et al 2007a).…”

Section: Introductionmentioning

confidence: 99%

Dense and warm molecular gas in the envelopes and outflows of southern low-mass protostars

Kempen

Hogerheijde

et al. 2009

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Context. Observations of dense molecular gas lie at the basis of our understanding of the density and temperature structure of protostellar envelopes and molecular outflows. The Atacama Pathfinder EXperiment (APEX) opens up the study of southern (Dec < −35 • ) protostars. Aims. We aim to characterize the properties of the protostellar envelope, molecular outflow and surrounding cloud, through observations of high excitation molecular lines within a sample of 16 southern sources presumed to be embedded YSOs, including the most luminous Class I objects in Corona Australis and Chamaeleon. Methods. Observations of submillimeter lines of CO, HCO + and their isotopologues, both single spectra and small maps (up to 80 × 80 ), were taken with the FLASH and APEX-2a instruments mounted on APEX to trace the gas around the sources. The HARP-B instrument on the JCMT was used to map IRAS 15398-3359 in these lines. HCO + mapping probes the presence of dense centrally condensed gas, a characteristic of protostellar envelopes. The rare isotopologues C 18 O and H 13 CO + are also included to determine the optical depth, column density, and source velocity. The combination of multiple CO transitions, such as 3-2, 4-3 and 7-6, allows to constrain outflow properties, in particular the temperature. Archival submillimeter continuum data are used to determine envelope masses. Results. Eleven of the sixteen sources have associated warm and/or dense (≥10 6 cm −3 ) quiescent gas characteristic of protostellar envelopes, or an associated outflow. Using the strength and degree of concentration of the HCO + 4-3 and CO 4-3 lines as a diagnostic, five sources classified as Class I based on their spectral energy distributions are found not to be embedded YSOs. The C 18 O 3-2 lines show that for none of the sources, foreground cloud layers are present. Strong molecular outflows are found around six sources, with outflow forces an order of magnitude higher than for previously studied Class I sources of similar luminosity. Conclusions. This study provides a starting point for future ALMA and Herschel surveys by identifying truly embedded southern YSOs and determining their larger scale envelope and outflow characteristics.