- ID:
- ivo://CDS.VizieR/J/ApJ/846/144
- Title:
- Virial analysis of the dense cores in Orion A
- Short Name:
- J/ApJ/846/144
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use data on gas temperature and velocity dispersion from the Green Bank Ammonia Survey and core masses and sizes from the James Clerk Maxwell Telescope Gould Belt Survey to estimate the virial states of dense cores within the Orion A molecular cloud. Surprisingly, we find that almost none of the dense cores are sufficiently massive to be bound when considering only the balance between self-gravity and the thermal and non-thermal motions present in the dense gas. Including the additional pressure binding imposed by the weight of the ambient molecular cloud material and additional smaller pressure terms, however, suggests that most of the dense cores are pressure-confined.
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- ID:
- ivo://CDS.VizieR/J/A+A/581/A140
- Title:
- VISTA Orion mini-survey
- Short Name:
- J/A+A/581/A140
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Orion cloud complex presents a variety of star formation mechanisms and properties and is still one of the most intriguing targets for star formation studies. We present VISTA/VIRCAM near-infrared observations of the L1630N star-forming region, including the stellar clusters NGC 2068 and NGC 2071 in the Orion molecular cloud B, and discuss them in combination with Spitzer data. We select 186 young stellar object (YSO) candidates in the region on the basis of multi-color criteria, confirm the YSO nature of the majority of them using published spectroscopy from the literature, and use this sample to investigate the overall star formation properties in L1630N. The K-band luminosity function of L1630N is remarkably similar to that of the Trapezium cluster, i.e., it presents a broad peak in the range 0.3-0.7M_{sun}_ and a fraction of substellar objects of ~20%. The fraction of YSOs still surrounded by disk/envelopes is very high (~85%) compared to other star-forming regions of similar age (1-2Myr), but includes some uncertain corrections for diskless YSOs. Yet, a possibly high disk fraction, together with the fact that 1/3 of the cloud mass has a gas surface density above the threshold for star formation (~129M_{sun}_/pc^2^), points toward a still ongoing star formation activity in L1630N. The star formation efficiency (SFE), star formation rate (SFR), and density of star formation of L1630N are within the ranges estimated for Galactic star-forming regions by the Spitzer "core to disk" and "Gould's Belt" surveys. However, the SFE and SFR are lower than the average value measured in the Orion A cloud and, in particular, lower than that in the southern regions of L1630. This might suggest different star formation mechanisms within the L1630 cloud complex.
- ID:
- ivo://CDS.VizieR/J/A+A/461/197
- Title:
- VLA NH3 observations of 5 IRAS sources
- Short Name:
- J/A+A/461/197
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The high angular resolution images with the Very Large Array (VLA) allow us to explore the general properties of protostellar cores in massive star forming regions at large distances. We observed the NH3 (J, K)=(1, 1) and (2, 2) lines toward five massive protostar candidates (IRAS 18196-1331, IRAS 18352-0148, IRAS 18361-0627, IRAS 18414-0339 and IRAS 19474+2637) with the VLA D configuration.
- ID:
- ivo://CDS.VizieR/J/A+A/610/A9
- Title:
- Water ice spectra toward the Pipe Nebula
- Short Name:
- J/A+A/610/A9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectroscopic studies of ices in nearby star-forming regions indicate that ice mantles form on dust grains in two distinct steps, starting with polar ice formation (H_2_O rich) and switching to apolar ice (CO rich). We test how well the picture applies to more diffuse and quiescent clouds where the formation of the first layers of ice mantles can be witnessed. Medium-resolution near-infrared spectra are obtained toward background field stars behind the Pipe Nebula. The water ice absorption is positively detected at 3.0um in seven lines of sight out of 21 sources for which observed spectra are successfully reduced. The peak optical depth of the water ice is significantly lower than those in Taurus with the same A_V_. The source with the highest water-ice optical depth shows CO ice absorption at 4.7um as well. The fractional abundance of CO ice with respect to water ice is 16+7-6%, and about half as much as the values typically seen in low-mass star-forming regions. A small fractional abundance of CO ice is consistent with some of the existing simulations. Observations of CO2 ice in the early diffuse phase of a cloud play a decisive role in understanding the switching mechanism between polar and apolar ice formation.
- ID:
- ivo://CDS.VizieR/J/ApJ/651/L125
- Title:
- Water masers associated with IR dark cloud cores
- Short Name:
- J/ApJ/651/L125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a survey of the 6_16_-5_23_ H_2_O maser transition toward a sample of 140 compact cores in infrared dark clouds using the Very Large Array. Strong (>1Jy) H_2_O maser emission was found associated with 17 cores, indicative of star formation in these cores. We infer that the cores with H2O masers have embedded protostars. Cores associated with maser emission have masses of 12 to 2x10^3^M_{sun}_, similar to the mass range in the entire sample. The H_2_O maser detection rate (12%) toward the compact, cold cores is much lower than that toward high-mass protostellar objects and ultracompact H ii regions. The detection rate of H_2_O masers is significantly higher for higher mass cores than for lower mass cores. We suggest that some of the most massive infrared dark cloud cores without H_2_O maser emission are at an evolutionary stage earlier than the protostellar phases. They are prime candidates for high-mass starless cores.
- ID:
- ivo://CDS.VizieR/J/ApJ/493/940
- Title:
- Water masers in Orion
- Short Name:
- J/ApJ/493/940
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Measurements of the 6_16_ -> 5_23_ line of H_2_O at 1.3cm in the Orion region of star formation are reported. With a spatial resolution of ~0.1", H_2_O maser emission was detected in two regions: Orion BN/KL and Orion S. The well-known masers in the BN/KL region are distributed in a 30"x30" area. The "shell" masers, within the BN/KL region, are distributed in a 2" by 0.5" strip centered on radio source I and are offset from IRc2.
- ID:
- ivo://CDS.VizieR/J/A+A/612/A5
- Title:
- W49B with H.E.S.S. and Fermi-LAT
- Short Name:
- J/A+A/612/A5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The supernova remnant (SNR) W49B originated from a core-collapse supernova that occurred between one and four thousand years ago, and subsequently evolved into a mixed-morphology remnant, which is interacting with molecular clouds (MC). Gamma-ray observations of SNR-MC associations are a powerful tool to constrain the origin of Galactic cosmic rays, as they can probe the acceleration of hadrons through their interaction with the surrounding medium and subsequent emission of non-thermal photons. We report the detection of a gamma-ray source coincident with W49B at very high energies (VHE; E>100GeV) with the H.E.S.S. Cherenkov telescopes together with a study of the source with five years of Fermi-LAT high-energy gamma-ray (0.06-300GeV) data. The smoothly connected, combined source spectrum, measured from 60MeV to multi-TeV energies, shows two significant spectral breaks at 304+/-20MeV and 8.4_-2.5_^+2.2^GeV; the latter is constrained by the joint fit from the two instruments. The detected spectral features are similar to those observed in several other SNR-MC associations and are found to be indicative of gamma-ray emission produced through neutral-pion decay.
- ID:
- ivo://CDS.VizieR/J/A+A/470/281
- Title:
- WFI optical photometry in Cha II dark cloud
- Short Name:
- J/A+A/470/281
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of an optical multi-band survey for low-mass pre-main sequence (PMS) stars and young brown dwarfs (BDs) in the Chamaeleon II (Cha II) dark cloud. This survey constitutes the complementary optical data to the c2d Spitzer Legacy survey in Cha II.
- ID:
- ivo://CDS.VizieR/J/ApJS/220/17
- Title:
- Wide-field NIR polarimetry of {rho} Oph cloud
- Short Name:
- J/ApJS/220/17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We conducted wide and deep simultaneous JHK_s_-band imaging polarimetry of the {rho} Ophiuchi cloud complex. Aperture polarimetry in the JHK_s_ band was conducted for 2136 sources in all three bands, of which 322 sources have significant polarizations in all the JHK_s_ bands and have been used for a discussion of the core magnetic fields. There is a positive correlation between degrees of polarization and H-K_s_ color up to H-K_s_~3.5. The magnetic field structures in the core region are revealed up to at least A_V_~47mag and are unambiguously defined in each sub-region (core) of Oph-A, Oph-B, Oph-C, Oph-E, Oph-F, and Oph-AC. Their directions, degrees of polarization, and polarization efficiencies differ but their changes are gradual; thus, the magnetic fields appear to be connected from core to core, rather than as a simple overlap of the different cloud core components. Comparing our results with the large-scale field structures obtained from previous optical polarimetric studies, we suggest that the magnetic field structures in the core were distorted by the cluster formation in this region, which may have been induced by shock compression due to wind/radiation from the Scorpius-Centaurus association.
- ID:
- ivo://CDS.VizieR/J/AJ/154/163
- Title:
- WISE-selected candidate SFRs beyond the Outer Arm
- Short Name:
- J/AJ/154/163
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The outer Galaxy beyond the Outer Arm provides a good opportunity to study star formation in an environment significantly different from that in the solar neighborhood. However, star-forming regions in the outer Galaxy have never been comprehensively studied or cataloged because of the difficulties in detecting them at such large distances. We studied 33 known young star-forming regions associated with 13 molecular clouds at R_G_>=13.5 kpc in the outer Galaxy with data from the Wide-field Infrared Survey Explorer (WISE) mid-infrared all-sky survey (Wright et al. 2010AJ....140.1868W; Jarrett et al. 2011ApJ...735..112J). From their color distribution, we developed a simple identification criterion of star-forming regions in the outer Galaxy with the WISE color. We applied the criterion to all the WISE sources in the molecular clouds in the outer Galaxy at R_G_>=13.5 kpc detected with the Five College Radio Astronomy Observatory (FCRAO) ^12^CO survey of the outer Galaxy (Heyer et al. 1998ApJS..115..241H), of which the survey region is 102.49{deg}=<l=<141.54{deg}, -3.03{deg}=<b=<5.41{deg}, and successfully identified 711 new candidate star-forming regions in 240 molecular clouds. The large number of samples enables us to perform the statistical study of star formation properties in the outer Galaxy for the first time. This study is crucial to investigate the fundamental star formation properties, including star formation rate, star formation efficiency, and initial mass function, in a primordial environment such as the early phase of the Galaxy formation.
