- ID:
- ivo://CDS.VizieR/J/ApJ/696/298
- Title:
- Dense cores in Perseus
- Short Name:
- J/ApJ/696/298
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the chemistry, temperature, and dynamical state of a sample of 193 dense cores or core candidates in the Perseus Molecular cloud and compare the properties of cores associated with young stars and clusters with those which are not. The combination of our NH3 and CCS observations with previous millimeter, submillimeter, and Spitzer data available for this cloud enables us both to determine core properties precisely and to accurately classify cores as starless or protostellar.
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- ID:
- ivo://CDS.VizieR/J/ApJ/668/1042
- Title:
- Dense cores in Perseus molecular cloud
- Short Name:
- J/ApJ/668/1042
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We survey the kinematics of over 150 candidate (and potentially star-forming) dense cores in the Perseus molecular cloud with pointed N_2_H^+^(1-0) and simultaneous C^18^O(2-1) observations. Our detection rate of N_2_H^+^ is 62%, rising to 84% for SCUBA-selected targets. In agreement with previous observations, we find that the dense N_2_H^+^ targets tend to display nearly thermal line widths, particularly those that appear to be starless (using Spitzer data), indicating that turbulent support on the small scales of molecular clouds is minimal. For those N_2_H^+^ targets that have an associated SCUBA dense core, we find that their internal motions are more than sufficient to provide support against the gravitational force on the cores.
- ID:
- ivo://CDS.VizieR/J/MNRAS/459/342
- Title:
- Dense cores in Taurus L1495 cloud
- Short Name:
- J/MNRAS/459/342
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalogue of dense cores in a ~4{deg}x2{deg} field of the Taurus star-forming region, inclusive of the L1495 cloud, derived from Herschel SPIRE and PACS observations in the 70{mu}m, 160{mu}m, 250{mu}m, 350{mu}m, and 500{mu}m continuum bands. Estimates of mean dust temperature and total mass are derived using modified blackbody fits to the spectral energy distributions. We detect 525 starless cores of which ~10-20 per cent are gravitationally bound and therefore presumably prestellar. Our census of unbound objects is ~85 per cent complete for M>0.015M_{sun}_ in low-density regions (A_V_<~5mag), while the bound (prestellar) subset is ~85 per cent complete for M>0.1M_{sun}_ overall. The prestellar core mass function (CMF) is consistent with lognormal form, resembling the stellar system initial mass function, as has been reported previously. All of the inferred prestellar cores lie on filamentary structures whose column densities exceed the expected threshold for filamentary collapse, in agreement with previous reports. Unlike the prestellar CMF, the unbound starless CMF is not lognormal, but instead is consistent with a power-law form below 0.3M_{sun}_ and shows no evidence for a low-mass turnover. It resembles previously reported mass distributions for CO clumps at low masses (M<~0.3M_{sun}_). The volume density PDF, however, is accurately lognormal except at high densities. It is consistent with the effects of self-gravity on magnetized supersonic turbulence. The only significant deviation from lognormality is a high-density tail which can be attributed unambiguously to prestellar cores.
- ID:
- ivo://CDS.VizieR/J/ApJ/665/1194
- Title:
- Dense cores in the Orion A cloud survey
- Short Name:
- J/ApJ/665/1194
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out an H^13^CO^+^ (J=1-0) core survey in a large area of 1.5degx0.5deg, covering the whole region of the Orion A molecular cloud, using the Nobeyama 45m radio telescope with the 25 Beam Array Receiver System (BEARS). This survey is unique in that a large area (~48pc^2^) of the cloud was covered with a high spatial resolution of 21" (0.05pc) and with a deep integration (1sigma~0.1K in T*_A_), resulting in a core mass detection of 1.6M_{sun}_. The morphology of the H^13^CO^+^ (J=1-0) emission is very similar to that of the 850um continuum emission. We identified 236 dense cores from our data with the clumpfind algorithm. The cores are close to virial equilibrium, independent of whether they are thermal or turbulent.
- ID:
- ivo://CDS.VizieR/J/ApJ/691/1560
- Title:
- Dense core survey in the Orion B cloud
- Short Name:
- J/ApJ/691/1560
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out an H^13^CO^+^(J=1-0 at 86.75433GHz) core survey in a large area of 1deg^2^, covering most of the dense region in the Orion B molecular cloud, using the Nobeyama 45m radio telescope with the 25-BEam Array Receiver System. We cataloged 151 dense cores using the clumpfind method. The cores have mean radius, velocity width, and mass of 0.10+/-0.02pc, 0.53+/-0.15km/s, and 8.1+/-6.4M_{sun}_, respectively, which are very similar to those in the Orion A cloud. We examined the spatial relation between our H^13^CO^+^ cores and the 850um cores observed by Johnstone and colleagues in 2001 (Cat. J/ApJ/559/307) and 2006 (Cat. J/ApJ/639/259), and found that there are two types of spatial relationships: H^13^CO^+^ cores with and without the 850um cores. Since the mean density of the 850um cores is higher than that of the H^13^CO^+^ cores, we can interpret the H^13^CO^+^ cores with 850um cores as being more centrally concentrated and hence more evolved, compared with those without.
- ID:
- ivo://CDS.VizieR/J/A+A/647/A42
- Title:
- Detected CH_2_ spectra
- Short Name:
- J/A+A/647/A42
- Date:
- 19 Jan 2022 13:29:47
- Publisher:
- CDS
- Description:
- The N_KaKc_=4_04_-3_13_ transitions of ortho-CH_2_ between 68 and 71GHz were first detected toward the Orion-KL and W51 Main star-forming regions. Given their high upper level energies (225K) above the ground state, they were naturally thought to arise in dense, hot molecular cores near newly formed stars. However, this has not been confirmed by further observations of these lines and their origin has remained unclear. Quite in general, only a paucity of observational data exist for CH_2_ and, while astrochemically an important compound, its actual occurrence in astronomical sources is poorly constrained. In this work, we aim to investigate the nature of the elusive CH_2_ emission and address its association with hot cores and examine alternative possibilities for its origin. Owing to its importance in carbon chemistry, we also extend the search for CH_2_ lines by observing an assortment of regions guided by the hypothesis that the observed CH_2_ emission likely arises from the hot gas environment of photodissociation regions (PDRs). We carried out observations using, first, the Kitt Peak 12m telescope to verify the original detection of CH_2_ toward different positions in the central region of Orion Molecular Cloud 1. These were followed-up by deep integrations using the higher angular resolution of the Onsala 20 m telescope. We have also searched for the N_KaKc_=2_12_-3_03_ transitions of para-CH_2_ between 440-445GHz toward the Orion giant molecular cloud complex using the APEX 12m telescope. We also obtained auxiliary data for carbon recombination lines with the Effelsberg 100m telescope and employed archival far infrared data. Our and other recent observations of the Orion region reported here, rule out an association with hot and dense gas. We find that the distribution of the CH_2_ emission follows closely that of the [CII] 158 um emission while CH_2_ is undetected toward the hot core itself. The observations suggest that its extended emission rather arises from hot but dilute layers of PDRs, but not from the denser parts of such regions, in particular the Orion Bar. This hypothesis was corroborated by comparisons of the observed CH_2_ line profiles with those of carbon radio recombination lines (CRRLs), well known PDR tracers. In addition, we report the detection of the 70GHz fine-, and hyperfine structure components of ortho-CH_2_ toward the W51 E, W51 M, W51 N, W49 N, W43, W75 N, DR21, and S140 star-forming regions, and three of the N_KaKc_=4_04_-3_13_ fine- and hyperfine structure transitions between 68-71GHz toward W3 IRS5. While we have no information on CH_2_'s spatial distribution in these regions, except for W51, we again see a correspondence of the profiles of CH_2_ lines with those of CRRLs. We see stronger CH_2_ emission toward the extended HII region W51 M than toward the much more massive and denser W51 E and N regions, strongly supporting an origin of CH_2_ in extended dilute gas. We also report the non-detection of the 2_12_-3_03_ transitions of para-CH_2_ toward Orion. Furthermore, using a non-LTE radiative transfer analysis, we can constrain the gas temperatures and H_2_ density to (163+/-26)K and (3.4+/-0.3)x10^3^cm^-3^, respectively, for the 68-71GHz ortho-CH_2_ transitions toward W3 IRS5, for which we have the highest quality data set. This analysis confirms our hypothesis that CH_2_ originates in warm and dilute PDR layers. Our analysis suggests that for the excitation conditions under the physical conditions that prevail in such an environment, these lines are masering, with weak level inversion. The resulting amplification of the lines' spontaneous emission greatly aides their detection.
- ID:
- ivo://CDS.VizieR/J/ApJ/770/L13
- Title:
- Detection of CH_3_COOCH_3_ in Orion
- Short Name:
- J/ApJ/770/L13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the discovery of methyl acetate, CH_3_COOCH_3_, through the detection of a large number of rotational lines from each one of the spin states of the molecule: AA species (A_1_ or A_2_), EA species (E_1_), AE species (E_2_), and EE species (E_3_ or E_4_). We also report, for the first time in space, the detection of the gauche conformer of ethyl formate, CH_3_CH_2_OCOH, in the same source. The trans conformer is also detected for the first time outside the Galactic center source SgrB2. From the derived velocity of the emission of methyl acetate, we conclude that it arises mainly from the compact ridge region with a total column density of (4.2+/-0.5)x10^15^/cm2. The derived rotational temperature is 150K. The column density for each conformer of ethyl formate, trans and gauche, is (4.5+/-1.0)x10^14^/cm2. Their abundance ratio indicates a kinetic temperature of 135K for the emitting gas and suggests that gas-phase reactions could participate efficiently in the formation of both conformers in addition to cold ice mantle reactions on the surface of dust grains.
- ID:
- ivo://CDS.VizieR/J/A+A/575/A87
- Title:
- Deuteration in massive star formation process
- Short Name:
- J/A+A/575/A87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An ever growing number of observational and theoretical evidence suggests that the deuterated fraction (column density ratio between a species containing D and its hydrogenated counterpart, Dfrac) is an evolutionary indicator both in the low- and the high-mass star formation process. However, the role of surface chemistry in these studies has not been quantified from an observational point of view. In order to compare how the deuterated fractions of species formed only in the gas and partially or uniquely on grain surfaces evolve with time, we observed rotational transitions of CH_3_OH, ^13^CH_3_OH, CH_2_DOH, CH_3_OD at 3 and 1.3mm, and of NH_2_D at 3mm with the IRAM-30m telescope, and the inversion transitions (1,1) and (2,2) of NH_3_ with the GBT, towards most of the cores already observed by Fontani et al. (2011A&A...529L...7F, 2014MNRAS.440..448F) in N_2_H^+^, N_2_D^+^, HNC, DNC. NH_2_D is detected in all but two cores, regardless of the evolutionary stage. Dfrac(NH_3_) is on average above 0.1, and does not change significantly from the earliest to the most evolved phases, although the highest average value is found in the protostellar phase (~0.3). Few lines of CH_2_DOH and CH_3_OD are clearly detected, and only towards protostellar cores or externally heated starless cores. This work clearly confirms an expected different evolutionary trend of the species formed exclusively in the gas (N_2_D^+^ and N_2_H^+^) and those formed partially (NH_2_D and NH_3_) or totally (CH_2_DOH and CH_3_OH) on grain mantles. The study also reinforces the idea that Dfrac(N_2_H^+^) is the best tracer of massive starless cores, while high values of Dfrac(CH_3_OH) seem rather good tracers of the early protostellar phases, at which the evaporation/sputtering of the grain mantles is most efficient.
- ID:
- ivo://CDS.VizieR/J/ApJ/878/151
- Title:
- DIB Measurements in 25 atlas sightlines
- Short Name:
- J/ApJ/878/151
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Aiming for a new and more comprehensive DIB catalog between 4000 and 9000{AA}, we revisited the Atlas Catalog based on the observations of HD 183143 and HD 204827. Twenty-five medium to highly reddened sight lines were selected, sampling a variety of spectral types of the background star and the interstellar environments. The median signal-to-noise ratio (S/N) of these spectra is ~1300 around 6400{AA}. Compared to the Atlas Catalog, 22 new DIBs were found, and the boundaries of 27 (sets of) DIBs were adjusted, resulting in an updated catalog containing 559 DIBs that we refer to as the Apache Point Observatory Catalog of Optical Diffuse Interstellar Bands. Measurements were then made based on this catalog. We found our survey most sensitive between 5500 and 7000{AA}, due largely to the local S/N of the spectra, the relative absence of interfering stellar lines, and the weakness of telluric residuals. For our data sample, the number of DIBs detected in a given sight line is mostly dependent on E_B-V_ and less on the spectral type of the background star. Some dependence on the molecular fraction f_H2_ is observed, but it is less well determined owing to the limited size of the data sample. The variations of the wavelengths of each DIB in different sight lines are generally larger than those of the known interstellar lines CH^+^, CH, and KI. Those variations could be due to the inherent error in the measurement, or to differences in the velocity components among sight lines.
- ID:
- ivo://CDS.VizieR/J/A+A/628/A85
- Title:
- Disk masses in the Orion Molecular Cloud-2
- Short Name:
- J/A+A/628/A85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mass evolution of protoplanetary disks is driven by internal processes and by external factors such as photoevaporation. Disentangling these two effects, however, remains difficult. We measured the dust masses of a sample of 132 disks in the Orion Molecular Cloud 2 (OMC-2) region, and compared them to externally photoevaporated disks in the Trapezium cluster, and to disks in nearby low-mass star-forming regions (SFRs). This allowed us to test whether initial disk properties are the same in high- and low-mass SFRs, and enabled a direct measurement of the effect of external photoevaporation on disks. A ~20'x4'mosaic of 3mm continuum observations from the Atacama Large Millimeter/submillimeter Array (ALMA) was used to measure the fluxes of 132 disks and 35 protostars >0.5pc away from the Trapezium. We identify and characterize a sample of 34 point sources not included in the Spitzer catalog on which the sample is based. Of the disks, 37 (28%) are detected, and have masses ranging from 7-270M_{sun}_. The detection rate for protostars is higher (69%). Disks near the Trapezium are found to be less massive by a factor 0.18^+0.18^_-0.11), implying a mass loss rate of 8x10^-8^M_{sun}_/yr. Our observations allow us to distinguish the impact of time and environment on disk evolution in a single SFR. The disk mass distribution in OMC-2 is statistically indistinguishable from that in nearby low-mass SFRs like Lupus and Taurus. We conclude that age is the main factor that determines the evolution of these disks. This result is robust with respect to assumptions of dust temperature, sample incompleteness, and biases. The difference between the OMC-2 and Trapezium cluster samples is consistent with mass loss driven by far-ultraviolet radiation near the Trapezium. Taken together, this implies that in isolation disk formation and evolution proceed similarly, regardless of cloud mass.
