M. Emprechtinger

The N2D+/N2H+ ratio as an evolutionary tracer of Class 0 protostars

Context. Deuterated ions, especially H2D + and N2D + , are abundant in cold (∼ 10 K), dense (∼ 10 5 cm −3 ) regions, in which CO is frozen out onto dust grains. In such environments, the N2D + /N2H + ratio can exceed the elemental abundance ratio of D/H by a factor of≃ 10 4 . Aims. We use the deuterium fractionation to investigate the evolutionary state of Class 0 protostars. In particular, we expec t the N2D + /N2H + ratio to decrease as temperature (a sign of the evolution of t he protostar) increases. Methods. We observed N2H + 1-0, N2D + 1-0, 2-1 and 3-2, C 18 O 1-0 and HCO + 3-2 in a sample of 20 Class 0 and borderline Class 0/I protostars. We determined the deuteration fraction and searched for correlations between the N2D + /N2H + ratio and well-established evolutionary tracers, such as TDust and the CO depletion factor. In addition, we compared the observational result with a chemical model. Results. In our protostellar sample, the N2H + 1-0 optical depths are significantly lower than those found i n prestellar cores, but the N2H + column densities are comparable, which can be explained by the higher temperature and larger line width in protostellar cores. The deuterium fractionation of N2H + in protostellar cores is also similar to that in prestellar c ores. We found a clear correlation between the N2D + /N2H + ratio and evolutionary tracers. As expected, the coolest, i.e. th e youngest, objects show the largest deuterium fractionation. Furthermore, we find that sources with a high N2D + /N2H + ratio show clear indication for infall (e.g.δv 0.15 even in the most evolved objects. Conclusions. The N2D + /N2H + ratio is known to trace the evolution of prestellar cores; we show that this ratio can be used to trace core evolution even after star formation. Protostars with an N 2D + /N2H + ratio above 0.15 are in a stage shortly after the beginning of collapse. Later on, deuterium fractionation decreases until it reaches a va lue of∼ 0.03 at the Class 0/I borderline.

First observations with CONDOR, a 1.5 THz heterodyne receiver

Context. The THz atmospheric “windows”, centered at roughly 1.3 and 1.5 THz, contain numerous spectral lines of astronomical importance, including three high-J CO lines, the [N II] line at 205 µm, and the ground transition of para-H2D + . The CO lines are tracers of hot (several 100 K), dense gas; [N II] is a cooling line of diffuse, ionized gas; the H2D + line is a non-depleting tracer of cold (∼20 K), dense gas. Aims. As the THz lines benefit the study of diverse phenomena (from high-mass star-forming regions to the WIM to cold prestellar cores), we have built the CO N + Deuterium Observations Receiver (CONDOR) to further explore the THz windows by ground-based observations. Methods. CONDOR was designed to be used at the Atacama Pathfinder EXperiment (APEX) and Stratospheric Observatory For Infrared Astronomy (SOFIA). CONDOR was installed at the APEX telescope, and test observations were made to characterize the instrument. Results. The combination of CONDOR on APEX successfully detected THz radiation from astronomical sources. CONDOR operated with typical Trec = 1600 K and spectral Allan variance times of ∼30 s. CONDOR’s “first light” observations of CO 13−12 emission from the hot core Orion FIR4 revealed a narrow line with TMB ≈ 210 K and ∆V ≈ 5. 4k m s −1 . A search for [N II] emission from the ionization front of the Orion Bar resulted in a non-detection. Conclusions. The successful deployment of CONDOR at APEX demonstrates the potential for making observations at THz frequencies from ground-based facilities.

Probable detection of H2D+ in the starless core Barnard 68

Context. The presence of H2D + in dense cloud cores underlies ion-molecule reactions that strongly enhance the deuterium fractionation of many molecular species. Aims. We determine the H2D + abundance in one starless core, Barnard 68, that has a particularly well established physical, chemical, and dynamical structure. Methods. We observed the ortho-H2D + ground-state line 110–111 ,t he N 2H + J = 4–3 line, and the H 13 CO + 4–3 line with the APEX telescope. Results. We report the probable detection of the o-H2D + line at an intensity Tmb = 0.22 ± 0.08 K and exclusively thermal line width, and find only upper limits to the N2H + 4–3 and H 13 CO + 4–3 intensities. Conclusions. Within the uncertainties in the chemical reaction rates and the collisional excitation rates, chemical model calculations and excitation simulations reproduce the observed intensities and that of o-H2D + in particular.

Spectroscopic investigation of unstudied southern PNe

We present a spectroscopic investigation of two hitherto unstudied galactic planetary nebulae (MeWe 1-10 and MeWe 1-11) and one candidate object (MeWe 2-5). The candidate object clearly has been identified as a bipolar hourglass-shaped PN. The galactic foreground extinction was derived and using photoionization models with CLOUDY the two round objects were classified as highly evolved nebulae.

Photoionization models of roughly circular Galactic planetary nebulae in the thick disk

We present the result of photo-ionizing modelling of the three planetary nebulae (PNe) A 20, A 15 and MeWe 1-3. All three objects are roughly circular, highly excited and have a high Galactic z. The PNe display low densities in the shell, but relatively dense halos. A low metallicity and a relative high electron temperature are found. Comparisons with radio observa- tions confirm the obtained properties. The objects very likely originate from thick disk stellar progenitors. The distances found investigating the PNe shells are somewhat lower than those derived spectroscopically for the central stars in the past.

Optical spectroscopy of IRAS 02091+6333

We present a detailed spectroscopic investigation, spanning four winters, of the asymptotic giant branch (AGB) star IRAS 02091+6333. Zijlstra & Weinberger (2002) found a giant wall of dust around this star and modelled this unique phenomenon. However their work suered from the quality of the optical investigations of the central object. Our spectroscopic investigation allowed us to define the spectral type and the interstellar foreground extinction more precisely. Accurate multi band photometry was carried out. This provides us with the possibility to derive the physical parameters of the system. The measurements presented here suggest a weak irregular photometric variability of the target, while there is no evidence of a spectroscopic variability over the last four years.

CONDOR observations of high mass star formation in Orion

CONDOR, the CO , N + , D euterium O bservations R eceiver, is designed to make velocity-resolved observations of the CO, [NII], and p-H 2 D + lines in the 1.4 THz (200-240μm) atmospheric windows. CONDORs first light observations were made with the APEX telescope in November 2005. The CONDOR beam on APEX (at ν = 1.5 THz) was expected to consist of a 4.3″ main beam and a 73″ error beam; this beam structure was verified from scans of Mars. The pointing accuracy, also determined from Mars scans, was better than 7″. The average atmospheric transmission during our Orion observations (elev~57°) was 19 ± 4% along the line-of-sight. A forward efficiency of F eff = 0.8 was determined from sky dips, and observations of the Moon and Mars were used to couple the CONDOR beam to sources of different sizes (η c = 0.40 and ~0.10, respectively). For more information, see Wiedner et al . 2006.

Probable detection of H2D

Context. The presence of H2D + in dense cloud cores underlies ion-molecule reactions that strongly enhance the deuterium fractionation of many molecular species. Aims. We determine the H2D + abundance in one starless core, Barnard 68, that has a particularly well established physical, chemical, and dynamical structure. Methods. We observed the ortho-H2D + ground-state line 110–111 ,t he N 2H + J = 4–3 line, and the H 13 CO + 4–3 line with the APEX telescope. Results. We report the probable detection of the o-H2D + line at an intensity Tmb = 0.22 ± 0.08 K and exclusively thermal line width, and find only upper limits to the N2H + 4–3 and H 13 CO + 4–3 intensities. Conclusions. Within the uncertainties in the chemical reaction rates and the collisional excitation rates, chemical model calculations and excitation simulations reproduce the observed intensities and that of o-H2D + in particular.

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Context. The presence of H2D + in dense cloud cores underlies ion-molecule reactions that strongly enhance the deuterium fractionation of many molecular species. Aims. We determine the H2D + abundance in one starless core, Barnard 68, that has a particularly well established physical, chemical, and dynamical structure. Methods. We observed the ortho-H2D + ground-state line 110–111 ,t he N 2H + J = 4–3 line, and the H 13 CO + 4–3 line with the APEX telescope. Results. We report the probable detection of the o-H2D + line at an intensity Tmb = 0.22 ± 0.08 K and exclusively thermal line width, and find only upper limits to the N2H + 4–3 and H 13 CO + 4–3 intensities. Conclusions. Within the uncertainties in the chemical reaction rates and the collisional excitation rates, chemical model calculations and excitation simulations reproduce the observed intensities and that of o-H2D + in particular.