Intermediate-mass Class Research Articles

Far-infrared line emission from the outer Galaxy cluster Gy 3–7 with SOFIA/FIFI-LS: Physical conditions and UV fields

Context. Far-infrared (FIR) line emission provides key information about the gas cooling and heating due to shocks and UV radiation associated with the early stages of star formation. Gas cooling via FIR lines might, however, depend on metallicity. Aims. We aim to quantify the FIR line emission and determine the spatial distribution of the CO rotational temperature, ultraviolet (UV) radiation field, and H2 number density toward the embedded cluster Gy 3–7 in the CMa–l224 star-forming region, whose metallicity is expected to be intermediate between that of the Large Magellanic Cloud and the Solar neighborhood. By comparing the total luminosities of CO and [OI] toward Gy 3–7 with values found for low- and high-mass protostars extending over a broad range of metallicities, we also aim to identify the possible effects of metallicity on the FIR line cooling within our Galaxy. Methods. We studied SOFIA/FIFI-LS spectra of Gy 3–7, covering several CO transitions from J = 14–13 to 31-30, the OH doublet at 79 μm, the [OI] 63.2 and 145.5 μm, and the [CII] 158 μm lines. The field of view covers a 2′ × 1′ region with a resolution of ~7″–18″. Results. The spatial extent of CO high-J (Jup ≥14) emission resembles that of the elongated 160 μm continuum emission detected with Herschel, but its peaks are offset from the positions of the dense cores. The [OI] lines at 63.2 μm and 145.5 μm follow a similar pattern, but their peaks are found closer to the positions of the cores. The CO transitions from J = 14–13 to J = 16–15 are detected throughout the cluster and show a median rotational temperature of 170 ± 30 K on Boltzmann diagrams. Comparisons to other protostars observed with Berschel show a good agreement with intermediate-mass sources in the inner Galaxy. Assuming an origin of the [OI] and high-J CO emission in UV-irradiated C–shocks, we obtained pre-shock H2 number densities of 104–105 cm−3 and UV radiation field strengths of 0.1–10 Habing fields (G0). Conclusions. Far-IR line observations reveal ongoing star formation in Gy 3–7, dominated by intermediate-mass Class 0/I young stellar objects. The ratio of molecular-to-atomic far-IR line emission shows a decreasing trend with bolometric luminosities of the protostars. However, it does not indicate that the low-metallicity has an impact on the line cooling in Gy 3–7.

IRS 31 14 in Vela C: Observations of wind driven turbulence

ABSTRACT We report three millimeter line observations of young stellar object (YSO) cluster IRAS 08563−4225 in the Vela C molecular cloud, detecting outflow aligned with an unidentified 2MASS infrared emission maximum. Emission features such as velocity dispersion ridges converging on intermediate mass Class I protostar IRS 31 14 indicate cluster wind driven turbulence, a scenario supported within an evolutionary framework derived from a range of star-forming regions. Prestellar–pre-main-sequence evolution is regulated by internal core turbulence and tracked on a Δ(σ2)–log ma diagram in four stages: disc formation, wind generation, outflow collimation, and birthline emergence, where ma = $\dot{M}_{\text{acc}}\, t_{\mathrm{out}}$ is a mass parameter given by $\dot{M}_{\text{acc}}$, the accretion rate and tout, the outflow dynamical time, and Δ(σ2) = log ($\frac{\sigma ^2_{\mathrm{outer}}}{\sigma ^2_{\mathrm{inner}}}$) with σinner, the inner and σouter, the outer core velocity dispersion. A turnover in Δ(σ2) indicates the generation of supersonic turbulence in star-forming regions with inner core collapse; in sets of low, intermediate, and high mass protostellar regions, a negative turbulent index at = $\frac{\text{d}{\Delta }\sigma ^2}{\text{dlog}m_a}$ corresponds to increasing age. Inner core collapse driven turbulence may apply at kiloparsec scales with turbulence amplification in a series of interacting YSO cluster cores in different evolutionary stages.

The prebiotic molecular inventory of Serpens SMM1

Aims. Methyl isocyanate (CH3NCO) and glycolonitrile (HOCH2CN) are isomers and prebiotic molecules that are involved in the formation of peptide structures and the nucleobase adenine, respectively. These two species are investigated to study the interstellar chemistry of cyanides (CN) and isocyanates (NCO) and to gain insight into the reservoir of interstellar prebiotic molecules. Methods. ALMA observations of the intermediate-mass Class 0 protostar Serpens SMM1-a and ALMA-PILS data of the low-mass Class 0 protostar IRAS 16293B are used. Spectra are analysed with the CASSIS line analysis software package in order to identify and characterise molecules. Results. CH3NCO, HOCH2CN, and various other molecules are detected towards SMM1-a. HOCH2CN is identified in the PILS data towards IRAS 16293B in a spectrum extracted at a half-beam offset position from the peak continuum. CH3NCO and HOCH2CN are equally abundant in SMM1-a at [X]/[CH3OH] of 5.3 × 10−4 and 6.2 × 10−4, respectively. A comparison between SMM1-a and IRAS 16293B shows that HOCH2CN and HNCO are more abundant in the former source, but CH3NCO abundances do not differ significantly. Data from other sources are used to show that the [CH3NCO]/[HNCO] ratio is similar in all these sources within ~10%. Conclusions. The new detections of CH3NCO and HOCH2CN are additional evidence for a large interstellar reservoir of prebiotic molecules that can contribute to the formation of biomolecules on planets. The equal abundances of these molecules in SMM1-a indicate that their formation is driven by kinetic processes instead of thermodynamic equilibrium, which would drive the chemistry to one product. HOCH2CN is found to be much more abundant in SMM1-a than in IRAS 16293B. From the observational data, it is difficult to indicate a formation pathway for HOCH2CN, but the thermal Strecker-like reaction of CN− with H2CO is a possibility. The similar [CH3NCO]/[HNCO] ratios found in the available sample of studied interstellar sources indicate that these two species are either chemically related or their formation is affected by physical conditions in the same way. Both species likely form early during star formation, presumably via ice mantle reactions taking place in the dark cloud or when ice mantles are being heated in the hot core. The relatively high abundances of HOCH2CN and HNCO in SMM1-a may be explained by a prolonged stage of relatively warm ice mantles, where thermal and energetic processing of HCN in the ice results in the efficient formation of both species.

Surveying the Giant H ii Regions of the Milky Way with SOFIA. II. M17

Abstract We present our second set of results from our mid-infrared imaging survey of Milky Way giant H ii regions. We used the FORCAST instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA) to obtain 20 and 37 μm images of the central ∼10′ × 10′ area of M17. We investigate the small- and large-scale properties of M17 using our data in conjunction with previous multiwavelength observations. The spectral energy distributions of individual compact sources were constructed with Spitzer-IRAC, SOFIA-FORCAST, and Herschel-PACS photometry data and fitted with massive young stellar object (MYSO) models. Seven sources were found to match the criteria for being MYSO candidates, four of which are identified here for the first time, and the stellar mass of the most massive object, UC 1, is determined to be 64 M ☉. We resolve the extended mid-infrared emission from the KW object and suggest that the angle of this extended emission is influenced by outflow. It is shown that IRS 5 decreases in brightness as a function of wavelength from the mid- to far-infrared and has several other indicators that point to it being an intermediate-mass Class II object and not an MYSO. We find that the large-scale appearance of emission in M17 at 20 μm is significantly affected by contamination from the [S iii] emission line from the ionized gas of the giant H ii region. Finally, a number of potential evolutionary tracers yield a consistent picture suggesting that the southern bar of M17 is likely younger than the northern bar.

Molecules in the Cep E-mm jet: evidence for shock-driven photochemistry?

ABSTRACT The chemical composition of protostellar jets and its origin are still badly understood. More observational constraints are needed to make progress. With that objective, we have carried out a systematic search for molecular species in the jet of Cep E-mm, a template for intermediate-mass Class 0 protostars, associated with a luminous, high-velocity outflow. We made use of an unbiased spectral line survey in the range 72–350 GHz obtained with the IRAM 30-m telescope, complementary observations of the CO J = 3–2 transition with the JCMT, and observations at 1 arcsec angular resolution of the CO J = 2–1 transition with the IRAM Plateau de Bure Interferometer. In addition to CO, we have detected rotational transitions from SiO, SO, H2CO, CS, HCO+, and HCN. A strong chemical differentiation is observed in the southern and northern lobes of the jet. Radiative transfer analysis in the large velocity gradient approximation yields typical molecular abundances of the order of 10−8 for all molecular species other than CO. Overall, the jets exhibit an unusual chemical composition, as CS, SO, and H2CO are found to be the most abundant species, with a typical abundance of (3–4)× 10−8. The transverse size of the CO jet emission estimated from interferometric observations is about 1000 au, suggesting that we are detecting emission from a turbulent layer of gas entrained by the jet in its propagation and not the jet itself. We propose that some molecular species could be the signatures of the specific photochemistry driven by the UV radiation field generated in the turbulent envelope.

First hot corino detected around an isolated intermediate-mass protostar: Cep E-mm

Context. Intermediate-mass (IM) protostars provide a bridge between the low- and high-mass protostars. Despite their relevance, little is known about their chemical diversity. Aims. We want to investigate the molecular richness towards the envelope of I-M protostars and to compare their properties with those of low- and high-mass sources. Methods. We have selected the isolated IM Class 0 protostar Cep E-mm to carry out an unbiased molecular survey with the IRAM 30 m telescope between 72 and 350 GHz with an angular resolution lying in the range 7–34″. Our goal is to obtain a census of the chemical content of the protostellar envelope. These data were complemented with NOEMA observations of the spectral bands 85.9–89.6 GHz and 216.8–220.4 GHz at angular resolutions of 2.3″ and 1.4″, respectively. Results. The 30 m spectra show bright emission of O- and N-bearing complex organic molecules (COMs): CH3OH and its rare isotopologues CH2DOH and 13CH3OH, CH3CHO, CH3OCH3, CH3COCH3, HCOOH, HCOOCH3, H2CCO, NH2CHO, CH3CN, C2H3CN, C2H5CN, HNCO and H2CO. We identify up to three components in the spectral signature of COMs: an extremely broad line (eBL) component associated with the outflowing gas (FWHM > 7kms−1), a narrow line (NL) component (FWHM < 3kms−1) associated with the cold envelope, and a broad line (BL) component (FWHM ≃ 5.5kms−1) which traces the signature of a hot corino. The eBL and NL components are detected only in molecular transitions of low excitation and dominate the emission of CH3OH. The BL component is detected in highly excited gas (Eup > 100 K). The NOEMA observations reveal Cep E-mm as a binary protostellar system, whose components, Cep E-A and Cep E-B, are separated by ≈1.7″. Cep E-A dominates the core continuum emission and powers the long-studied, well-known, high-velocity jet associated with HH377. The lower flux source Cep E-B powers another high-velocity molecular jet, reaching velocities of ≈80 km s−1, which propagates in a direction close to perpendicular with respect to the Cep E-A jet. Our interferometric maps show that the emission of COMs arises from a region of ≈0.7″ size around Cep E-A, and corresponds to the BL component detected with the IRAM 30 m telescope. On the contrary, no COM emission is detected towards Cep E-B. We have determined the rotational temperature (Trot) and the molecular gas column densities from a simple population diagram analysis or assuming a given excitation temperature. Rotational temperatures of COMs emission were found to lie in the range 20−40 K with column densities ranging from a few times 1015 cm−2 for O-bearing species, down to a few times 1014 cm−2 for N-bearing species. Molecular abundances are similar to those measured towards other low- and intermediate-mass protostars. Ketene (H2CCO) appears as an exception, as it is found significantly more abundant towards Cep E-A. High-mass hot cores are significantly less abundant in methanol and N-bearing species are more abundant by two to three orders of magnitude. Conclusions. Cep E-mm reveals itself as a binary protostellar system with a strong chemical differentiation between both cores. Only the brightest component of the binary is associated with a hot corino. Its properties are similar to those of low-mass hot corinos.

Nature of shocks revealed by SOFIA OI observations in the Cepheus E protostellar outflow

Context.Protostellar jets and outflows are key features of the star-formation process, and primary processes of the feedback of young stars on the interstellar medium. Understanding the underlying shocks is necessary to explain how jet and outflow systems are launched, and to quantify their chemical and energetic impacts on the surrounding medium.Aims.We performed a high-spectral resolution study of the [OI]63μmemission in the outflow of the intermediate-mass Class 0 protostar Cep E-mm. The goal is to determine the structure of the outflow, to constrain the chemical conditions in the various components, and to understand the nature of the underlying shocks, thus probing the origin of the mass-loss phenomenon.Methods.We present observations of the O i3P1→3P2, OH between2Π1/2J= 3/2 andJ= 1/2 at 1837.8 GHz, and CO (16–15) lines with the GREAT receiver onboard SOFIA towards three positions in the Cep E protostellar outflow: Cep E-mm (the driving protostar), Cep E-BI (in the southern lobe), and Cep E-BII (the terminal position in the southern lobe).Results.The CO (16–15) line is detected at all three positions. The [OI]63μmline is detected in Cep E-BI and BII, whereas the OH line is not detected. In Cep E-BII, we identify three kinematical components in O iand CO. These were already detected in CO transitions and relate to spatial components: the jet, the HH377 terminal bow-shock, and the outflow cavity. We measure line temperature and line integrated intensity ratios for all components. The O icolumn density is higher in the outflow cavity than in the jet, which itself is higher than in the terminal shock. The terminal shock is the region where the abundance ratio of O ito CO is the lowest (about 0.2), whereas the jet component is atomic (N(O i)/N(CO) ~ 2.7). In the jet, we compare the [OI]63μmobservations with shock models that successfully fit the integrated intensity of 10 CO lines. We find that these models most likely do not fit the [OI]63μmdata.Conclusions.The high intensity of O iemission points towards the propagation of additional dissociative or alternative FUV-irradiated shocks, where the illumination comes from the shock itself. A picture emerges from the sample of low-to-high mass protostellar outflows, where similar observations have been performed, with the effects of illumination increasing with the mass of the protostar. These findings need confirmation with more observational constraints and a larger sample.

The structure of the Cepheus E protostellar outflow: The jet, the bowshock, and the cavity

Context. Protostellar outflows are a crucial ingredient of the star-formation process. However, the physical conditions in the warm outflowing gas are still poorly known.Aims. We present a multi-transition, high spectral resolution CO study of the outflow of the intermediate-mass Class 0 protostar Cep E-mm. The goal is to determine the structure of the outflow and to constrain the physical conditions of the various components in order to understand the origin of the mass-loss phenomenon.Methods. We have observed the J = 12–11, J = 13–12, and J = 16–15 CO lines at high spectral resolution with SOFIA/GREAT and the J = 5–4, J = 9–8, and J = 14–13 CO lines with HIFI/Herschel towards the position of the terminal bowshock HH377 in the southern outflow lobe. These observations were complemented with maps of CO transitions obtained with the IRAM 30 m telescope (J = 1–0, 2–1), the Plateau de Bure interferometer (J = 2–1), and the James Clerk Maxwell Telescope (J = 3–2, 4–3).Results. We identify three main components in the protostellar outflow: the jet, the cavity, and the bowshock, with a typical size of 1.7″ × 21″, 4.5″, and 22″ × 10″, respectively. In the jet, the emission from the low-J CO lines is dominated by a gas layer at T kin = 80–100 K, column density N (CO) = 9 × 1016 cm-2 , and density n (H2 ) = (0.5−1) × 105 cm-3 ; the emission of the high-J CO lines arises from a warmer (T kin = 400–750 K), denser (n (H2 ) = (0.5−1) × 106 cm-3 ), lower column density (N (CO) = 1.5 × 1016 cm-2 ) gas component. Similarly, in the outflow cavity, two components are detected: the emission of the low-J lines is dominated by a gas layer of column density N (CO) = 7 × 1017 cm-2 at T kin = 55–85 K and density in the range (1−8) × 105 cm-3 ; the emission of the high-J lines is dominated by a hot, denser gas layer with T kin = 500–1500K, n (H2 ) = (1−5) × 106 cm-3 , and N (CO) = 6 × 1016 cm-2 . A temperature gradient as a function of the velocity is found in the high-excitation gas component. In the terminal bowshock HH377, we detect gas of moderate excitation, with a temperature in the range T kin ≈ 400–500 K, density n (H2 ) ≃ (1 −2) × 106 cm-3 and column density N (CO) = 1017 cm-2 . The amounts of momentum carried away in the jet and in the entrained ambient medium are similar. Comparison with time-dependent shock models shows that the hot gas emission in the jet is well accounted for by a magnetized shock with an age of 220–740 yr propagating at 20–30 km s-1 in a medium of density n (H2 ) = (0.5−1) × 105 cm-3 , consistent with that of the bulk material.Conclusions. The Cep E protostellar outflow appears to be a convincing case of jet bowshock driven outflow. Our observations trace the recent impact of the protostellar jet into the ambient cloud, produing a non-stationary magnetized shock, which drives the formation of an outflow cavity.

MASSIVE STAR FORMATION AT THE PERIPHERY OF THE EVOLVED GIANT H II REGION W 39

We present the first detailed study of the large, ~30 pc diameter, inner-Galaxy HII region W 39. Radio recombination line observations combined with HI absorption spectra and Galactic rotation models show that the region lies at V(LSR) = +65.4+/-0.5 km/s corresponding to a near kinematic distance of 4.5+/-0.2 kpc. Analysis of radio continuum emission shows that the HII region is being powered by a cluster of OB stars with a combined hydrogen-ionizing luminosity of log(Q) >=50, and that there are three compact HII regions located on the periphery of W 39, each with log(Q)~48.5 (single O7 - O9 V star equivalent). In the infrared, W 39 has a hierarchical bubble morphology, and is a likely site of sequential star formation involving massive stars. Kinematic models of the expansion of W 39 yield timescales of order Myr consistent with a scenario where the formation of the smaller HII regions has been triggered by the expansion of W 39. Using Spitzer GLIMPSE and MIPSGAL data we show that star-formation activity is not distributed uniformly around the periphery of W 39 but is concentrated in two areas that include the compact HII regions as well as a number of intermediate-mass Class I and Class II YSOs.

High-JCO emission in the Cepheus E protostellar outflow observed with SOFIA/GREAT

We present and analyze two spectrally resolved high-J CO lines towards the molecular outflow Cep E, driven by an intermediate-mass class 0 protostar. Using the GREAT receiver on board SOFIA, we observed the CO (12--11) and (13--12) transitions (E_u ~ 430 and 500 K, respectively) towards one position in the blue lobe of this outflow, that had been known to display high-velocity molecular emission. We detect the outflow emission in both transitions, up to extremely high velocities (~ 100 km/s with respect to the systemic velocity). We divide the line profiles into three velocity ranges that each have interesting spectral features: standard, intermediate, and extremely high-velocity. One distinct bullet is detected in each of the last two. A large velocity gradient analysis for these three velocity ranges provides constraints on the kinetic temperature and volume density of the emitting gas, >~ 100 K and > ~ 10^4 cm^-3, respectively. These results are in agreement with previous ISO observations and are comparable with results obtained by Herschel for similar objects. We conclude that high-J CO lines are a good tracer of molecular bullets in protostellar outflows. Our analysis suggests that different physical conditions are at work in the intermediate velocity range compared with the standard and extremely high-velocity gas at the observed position.

Shocked water in the Cepheus E protostellar outflow

Previous far-infrared observations at low-angular resolution have reported the presence of water associated with low-velocity outflow shocks and protostellar envelopes. The outflow driven by the intermediate-mass class 0 protostar Cep E is among the most luminous outflows detected so far. Using the IRAM 30m telescope, we searched for and detected the para-water line emission at 183 GHz in the Cep E star-forming core. The emission arises from high-velocity gas close to the protostar, which is unresolved in the main beam of the telescope. Complementary observations at 2" resolution with the Plateau de Bure interferometer helped establish the origin of the emission detected and the physical conditions in the emitting gas. The water line profile and its spatial distribution are very similar to those of SiO. We find that the water emission arises from warm ($\sim 200\K$), dense ($(1-2)\times 10^6\cmmt$) gas, and its abundance is enhanced by one to two orders of magnitude with respect to the protostellar envelope. We detect water emission in strong shocks from the high-velocity jet at 1000 AU from the protostar. Despite the large beam size of the telescope, such emission should be detectable with Herschel.

Chemical study of intermediate-mass (IM) Class 0 protostars

Chemical study of intermediate-mass (IM) Class 0 protostars

A PRECISE MASS MEASUREMENT OF THE INTERMEDIATE-MASS BINARY PULSAR PSR J1802 – 2124

PSR J1802 − 2124 is a 12.6 ms pulsar in a 16.8 hr binary orbit with a relatively massive white dwarf (WD) companion. These properties make it a member of the intermediate-mass class of binary pulsar (IMBP) systems. We have been timing this pulsar since its discovery in 2002. Concentrated observations at the Green Bank Telescope, augmented with data from the Parkes and Nançay observatories, have allowed us to determine the general relativistic Shapiro delay. This has yielded pulsar and WD mass measurements of 1.24 ± 0.11 M☉ and 0.78 ± 0.04 M☉ (68% confidence), respectively. The low mass of the pulsar, the high mass of the WD companion, the short orbital period, and the pulsar spin period may be explained by the system having gone through a common-envelope phase in its evolution. We argue that selection effects may contribute to the relatively small number of known IMBPs.

Protostellar clusters in intermediate mass (IM) star forming regions

Context. The transition between the low density groups of T Tauri stars and the high density clusters around massive stars occurs in the intermediate-mass (IM) range ($M_*\sim2{-}8~M_\odot$). High spatial resolution studies of IM young stellar objects (YSO) can provide important clues to understand the clustering in massive star forming regions. Aims. Our aim is to search for clustering in IM Class 0 protostars. The high spatial resolution and sensitivity provided by the new A configuration of the Plateau de Bure Interferometer (PdBI) allow us to study the clustering in these nearby objects. Methods. We have imaged three IM Class 0 protostars (Serpens-FIRS 1, IC 1396 N, CB 3) in the continuum at 3.3 and 1.3 mm using the PdBI. The sources have been selected with different luminosity to investigate the dependence of the clustering process on the luminosity of the source. Results. Only one millimeter (mm) source is detected towards the low luminosity source Serpens-FIRS 1. Towards CB 3 and IC1396 N, we detect two compact sources separated by ~0.05 pc. The 1.3 mm image of IC 1396 N, which provides the highest spatial resolution, reveal that one of these cores is splitted in, at least, three individual sources.

Who is eating the outflow? High-angular resolution study of an intermediate-mass protostar in L1206

Up to now only a few intermediate-mass molecular outflows have been studied with enough high-angular resolution. The aim of this work is to study in detail the intermediate-mass YSO IRAS 22272+6358A, which is embedded in L1206, and its molecular outflow, in order to investigate the interaction of the outflow with the dense protostellar material, and to compare their properties with those of lower mas counterparts. We carried out OVRO observations of the 2.7 mm continuum emission, CO(1-0), C18O(1-0), and HC3N(12-11) in order to map with high-angular resolution the core of L1206, and to derive the properties of the dust emission, the molecular outflow and the dense protostellar envelope. The 2.7 mm continuum emission has been resolved into four sources, labeled OVRO~1, 2, 3, and 4. The intermediate-mass Class~0/I object OVRO 2, with a mass traced by the dust emission of 14.2 Msun, is the source associated with IRAS 22272+6358A. The CO(1-0) observations have revealed a very collimated outflow driven by OVRO 2, at a PA ~140 degr, that has a very weak southeastern red lobe and a much stronger northwestern blue lobe. Photodissociation toward the red lobe produced by the ionization front coming from the bright-rimmed diffuse HII region could be responsible of the morphology of the outflow. The spatial correlation between the outflow and the elongated dense protostellar material traced by HC3N(12-11) suggests an interaction between the molecular outflow and the protostellar envelope. Shocks produced by the molecular outflow, and possibly by the shock front preceding the ionization front could account for the southern enhancement of HC3N. The properties of the intermediate-mass protostar OVRO 2 and the molecular outflow are consistent with those of lower mass counterparts.

Spitzerand Magellan Observations of NGC 2264: A Remarkable Star‐forming Core near IRS 2

We analyze {\it Spitzer} and Magellan observations of a star forming core near IRS-2 in the young cluster NGC 2264. The submillimeter source IRAS 12 S1, previously believed to be an intermediate mass Class 0 object is shown to be a dense collection of embedded, low mass stars. We argue that this group of stars represents the fragmenting collapse of a dense, turbulent core, based on a number of indicators of extreme youth. With reasonable estimates for the velocity dispersion in the group, we estimate a dynamical lifetime of only a few x 10$^{4}$ years. Spectral energy distributions of stars in the core are consistent with Class I or Class 0 assignments. We present observations of an extensive system of molecular hydrogen emission knots. The luminosity of the objects in the core region are consistent with roughly solar mass protostars.

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

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 –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 HO 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 H2O-rich CO likely correlates with that of water ice. A weak feature at 3.54 μm attributed to solid CHOH and a broad feature near 4.62 μm are observed toward LLN 17, but not toward the other sources. The derived abundances of solid CHOH and OCN- are ~% and ~% of the HO ice abundance respectively. The HO 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.

Detection of a hot core in the intermediate-mass Class 0 protostar NGC 7129–FIRS 2

We report high angular resolution (HPBW ∼ 0.6 �� × 0.5 �� at 1.3 mm) observations of the Class 0 intermediate-mass (IM) protostar NGC 7129- FIRS 2 using the Plateau de Bure Interferometer. Our observations show the existence of an intense unresolved source in the continuum at 1.3 mm and 3 mm at the position of the Class 0 object. In addition, compact CH3CN emission is detected at this position. The high rotational temperature derived from the CH3CN lines (Trot ≈ 50 K), as well as the enhanced CH3CN fractional abundance (X(CH3CN) ∼ 7.0×10 −9 ), shows the existence of a hot core in this IM young stellar object. This is to our knowledge the first IM hot core detected so far. Interferometric maps of the region in the CH3OH 5kk� →4kkand D2CO 404→303 lines are also presented in this paper. The methanol emission presents two condensations, one associated with the hot core, which was very intense in the high upper state energy lines (Eu > 100 K), and the other associated with the bipolar outflow which dominates the emission in the low excitation lines. Enhanced CH3OH abundances (X(CH3OH) ∼ 3 × 10 −8 -af ew 10 −7 ) were measured in both components. While intense D2CO 404 → 303 emission was detected towards the hot core, the N2D + 3 → 2 line was not detected in our interferometric observations. The different behaviors of D2CO and N2D + emissions suggest different formation mechanisms for the two species and different deuteration processes for H2CO and N2H + (surface and gas-phase chemistry, respectively). Finally, the spectrum of the large bandwidth correlator shows a forest of lines at the hot core position, revealing that this object is extraordinarily rich in complex molecules. For deeper insight into the chemistry of complex molecules, we compared the fractional abundances of the complex O- and N- bearing species in FIRS 2 with those in hot corinos and massive hot cores. Within the large uncertainty involved in fractional abundance estimates towards hot cores, we did not detect any variation in the relative abundances of O- and N-bearing molecules ((CH3CN)/(CH3OH)) with the hot core luminosity. However, the O-bearing species H2CO and HCOOH seemed to be more abundant in low and intermediate mass stars than in massive star-forming regions. We propose that this could be the consequence of a different grain mantle composition in low and massive star-forming regions.

Proper motion of H2O masers in IRAS 20050+2720 MMS1: an AU scale jet associated with an intermediate-mass class 0 source

We conducted a 4 epoch, 3 month, VLBA proper motion study of H 2 O masers toward an intermediate-mass class 0 source IRAS 20050+2720 MMS1 (d = 700 pc). The region of IRAS 20050+2720 contains at least 3 bright young stellar objects at millimeter to submillimeter wavelengths and shows three pairs of CO outflow lobes: the brightest source MMS1, which shows an extremely high velocity (EHV) wing emission, is believed to drive the outflow(s). From milli-arcsecond (mas) resolution VLBA images, we found two groups of H 2 O maser spots at the center of the submillimeter core of MMS I. One group consists of more than ∼50 intense maser spots; the other group consisting of several weaker maser spots is located at 18 AU south-west of the intense group. Distribution of the maser spots in the intense group shows an arc-shaped structure which includes the maser spots that showed a clear velocity gradient. The spatial and velocity structures of the maser spots in the arc-shape did not significantly change through the 4 epochs. Furthermore, we found a relative proper motion between the two groups. Their projected separation increased by 1.13 ± 0.11 mas over the 4 epochs along a line connecting them (corresponding to a transverse velocity of 14.4 km s -1 ). The spatial and velocity structures of the intense group and the relative proper motions strongly suggest that the maser emission is associated with a protostellar jet. Comparing the observed LSR velocities with calculated radial velocities from a simple biconical jet model, we conclude that the most of the maser emission is likely to be associated with an accelerating biconical jet that has large opening angle of about 70°. The large opening angle of the jet traced by the masers would support the hypothesis that poor jet collimation is an inherent property of luminous (proto)stars.

INTERMEDIATE-MASS BLACK HOLES

The mathematical simplicity of black holes, combined with their links to some of the most energetic events in the universe, means that black holes are key objects for fundamental physics and astrophysics. Until recently, it was generally believed that black holes in nature appear in two broad mass ranges: stellar-mass (M~3–20 M⊙), which are produced by the core collapse of massive stars, and supermassive (M~106–1010 M⊙), which are found in the centers of galaxies and are produced by a still uncertain combination of processes. In the last few years, however, evidence has accumulated for an intermediate-mass class of black holes, with M~102–104 M⊙. If such objects exist they have important implications for the dynamics of stellar clusters, the formation of supermassive black holes, and the production and detection of gravitational waves. We review the evidence for intermediate-mass black holes and discuss future observational and theoretical work that will help clarify numerous outstanding questions about these objects.