NGC 7129 FIRS 2 (hereafter FIRS 2) is an intermediate-mass (2 to 8 Msun) protostar located at a distance of 1250 pc. High spatial resolution observations are required to resolve the hot core at its center. We present a molecular survey from 218200 MH
z to 221800 MHz carried out with the IRAM Plateau de Bure Interferometer. These observations were complemented with a long integration single-dish spectrum taken with the IRAM 30m telescope. We used a Local Thermodynamic Equilibrium (LTE) single temperature code to model the whole dataset. The interferometric spectrum is crowded with a total of ~300 lines from which a few dozens remain unidentified yet. The spectrum has been modeled with a total of 20 species and their isomers, isotopologues and deuterated compounds. Complex molecules like methyl formate (CH3OCHO), ethanol (CH3CH2OH), glycolaldehyde (CH2OHCHO), acetone (CH3COCH3), dimethyl ether (CH3OCH3), ethyl cyanide (CH3CH2CN) and the aGg conformer of ethylene glycol (aGg-(CH2OH)_2) are among the detected species. The detection of vibrationally excited lines of CH3CN, CH3OCHO, CH3OH, OCS, HC3N and CH3CHO proves the existence of gas and dust at high temperatures. In fact, the gas kinetic temperature estimated from the vibrational lines of CH3CN, ~405 K, is similar to that measured in massive hot cores. Our data allow an extensive comparison of the chemistry in FIRS~2 and the Orion hot core. We find a quite similar chemistry in FIRS 2 and Orion. Most of the studied fractional molecular abundances agree within a factor of 5. Larger differences are only found for the deuterated compounds D2CO and CH2DOH and a few molecules (CH3CH2CN, SO2, HNCO and CH3CHO). Since the physical conditions are similar in both hot cores, only different initial conditions (warmer pre-collapse phase in the case of Orion) and/or different crossing time of the gas in the hot core can explain this behavior.
The Plateau de Bure Interferometer has been used to map the continuum emission at 3.4 mm and 1.1 mm together with the J=1->0 and J=3->2 lines of HCN and HCO+ towards the binary star GV Tau. The 3.4 mm observations did not resolve the binary component
s and the HCN J=1->0 and HCO+ J=1->0 line emissions trace the circumbinary disk and the flattened envelope. However, the 1.1 mm observations resolved the individual disks of GV Tau N and GV Tau S and allowed us to study their chemistry. We detected the HCN 3->2 line only towards the individual disk of GV Tau N, and the emission of the HCO+ 3->2 line towards GV Tau S. Simple calculations indicate that the 3->2 line of HCN is formed in the inner R<12 AU of the disk around GV Tau N where the HCN/HCO+ abundance ratio is >300. On the contrary, this ratio is <1.6 in the disk around GV Tau S. The high HCN abundance measured in GV Tau N is well explained by photo-chemical processes in the warm (>400K) and dense disk surface.
NGC 7129 FIRS 2 is a young intermediate-mass (IM) protostar, which is associated with two energetic bipolar outflows and displays clear signs of the presence of a hot core. It has been extensively observed with ground based telescopes and within the
WISH Guaranteed Time Herschel Key Program. We present new observations of the C18O 3-2 and the HDO 3_{12}-2_{21} lines towards NGC 7129 FIRS 2. Combining these observations with Herschel data and modeling their emissions, we constrain the C18O and HDO abundance profiles across the protostellar envelope. In particular, we derive the abundance of C18O and HDO in the hot core. The intensities of the C18O lines are well reproduced assuming that the C18O abundance decreases through the protostellar envelope from the outer edge towards the centre until the point where the gas and dust reach the CO evaporation temperature (~20-25 K) where the C18O is released back to the gas phase. Once the C18O is released to the gas phase, the modelled C18O abundance is found to be ~1.6x10^{-8}, which is a factor of 10 lower than the reference abundance. This result is supported by the non-detection of C18O 9-8, which proves that even in the hot core (T_k>100 K) the CO abundance must be 10 times lower than the reference value. Several scenarios are discussed to explain this C18O deficiency. One possible explanation is that during the pre-stellar and protostellar phase, the CO is removed from the grain mantles by reactions to form more complex molecules. Our HDO modeling shows that the emission of HDO 3_{12}-2_{21} line is maser and comes from the hot core (T_k>100 K). Assuming the physical structure derived by Crimier et al. (2010), we determine a HDO abundance of ~0.4 - 1x10^{-7} in the hot core of this IM protostar, similar to that found in the hot corinos NGC 1333 IRAS 2A and IRAS 16293-2422.
Very few molecular species have been detected in circumstellar disks surrounding young stellar objects. We are carrying out an observational study of the chemistry of circumstellar disks surrounding T Tauri and Herbig Ae stars. First results of this
study are presented in this note. We used the EMIR receivers recently installed at the IRAM 30m telescope to carry a sensitive search for molecular lines in the disks surrounding AB Aur, DM Tau, and LkCa 15. We detected lines of the molecules HCO+, CN, H2CO, SO, CS, and HCN toward AB Aur. In addition, we tentatively detected DCO+ and H2S lines. The line profiles suggest that the CN, HCN, H2CO, CS and SO lines arise in the disk. This makes it the first detection of SO in a circumstellar disk. We have unsuccessfully searched for SO toward DM Tau and LkCa 15, and for c-C3H2 toward AB Aur, DM Tau, and LkCa 15. Our upper limits show that contrary to all the molecular species observed so far, SO is not as abundant in DM Tau as it is in AB Aur. Our results demonstrate that the disk associated with AB Aur is rich in molecular species. Our chemical model shows that the detection of SO is consistent with that expected from a very young disk where the molecular adsorption onto grains does not yet dominate the chemistry.
Mon R2, at a distance of 830 pc, is the only ultracompact HII region (UC HII) where the photon-dominated region (PDR) between the ionized gas and the molecular cloud can be resolved with Herschel. HIFI observations of the abundant compounds 13CO, C18
O, o-H2-18O, HCO+, CS, CH, and NH have been used to derive the physical and chemical conditions in the PDR, in particular the water abundance. The 13CO, C18O, o-H2-18O, HCO+ and CS observations are well described assuming that the emission is coming from a dense (n=5E6 cm-3, N(H2)>1E22 cm-2) layer of molecular gas around the UC HII. Based on our o-H2-18O observations, we estimate an o-H2O abundance of ~2E-8. This is the average ortho-water abundance in the PDR. Additional H2-18O and/or water lines are required to derive the water abundance profile. A lower density envelope (n~1E5 cm-3, N(H2)=2-5E22 cm-2) is responsible for the absorption in the NH 1_1-0_2 line. The emission of the CH ground state triplet is coming from both regions with a complex and self-absorbed profile in the main component. The radiative transfer modeling shows that the 13CO and HCO+ line profiles are consistent with an expansion of the molecular gas with a velocity law, v_e =0.5 x (r/Rout)^{-1} km/s, although the expansion velocity is poorly constrained by the observations presented here.
Water is a key species in many astrophysical environments, but it is particularly important in proto-planetary disks. So far,observations of water in these objects have been scarce, but the situation should soon change thanks to the Herschel satellit
e. We report here a theoretical study of the water line spectrum of a proto-planetary disk surrounding Ae stars. We show that several lines will be observable with the HIFI instrument onboard the Herschel Space Observatory. We predict that some maser lines could also be observable with ground telescopes and we discuss how the predictions depend not only on the adopted physical and chemical model but also on the set of collisional coefficients used and on the H2 ortho to para ratio through its effect on collisional excitation. This makes the water lines observations a powerful, but dangerous -if misused- diagnostic tool.
The molecular gas composition in the inner 1 kpc disk of the starburst galaxy M82 resembles that of Galactic Photon Dominated Regions (PDRs). In particular, large abundances of the reactive ions HOC+ and CO+ have been measured in the nucleus of this
galaxy. To investigate the origin of the large abundances of reactive ions in M82, we have completed our previous 30m HOC+ J=1-0 observations with the higher excitation HCO+ and HOC+ J=4-3 and 3-2 rotational lines. In addition, we have obtained with the IRAM Plateau de Bure Interferometer (PdBI) a 4 resolution map of the HOC+ 1-0 emission, the first ever obtained in a Galactic or extragalactic source. Our HOC+ interferometric image shows that the emission of the HOC+ 1-0 line is mainly restricted to the nuclear disk, with the maxima towards the E. and W. molecular peaks. In addition, line excitation calculations imply that the HOC+ emission arises in dense gas. Therefore, the HOC+ emission is arising in the dense PDRs embedded in the M82 nuclear disk, rather than in the intercloud phase and/or wind. We have improved our previous chemical model of M82 by (i) using the new version of the Meudon PDR code, (ii) updating the chemical network, and (iii) considering two different types of clouds (with different thickness). Most molecular observations (HCO+, HOC+, CO+, CN, HCN, H3O+) are well explained assuming that ~ 87 % of the mass of the molecular gas is forming small clouds (Av=5 mag) while only ~ 13 % of the mass is in large molecular clouds (Av=50 mag). Such small number of large molecular clouds suggests that M82 is an old starburst, where star formation has almost exhausted the molecular gas reservoir.
