- ID:
- ivo://CDS.VizieR/J/A+A/602/A77
- Title:
- HOBYS: 46 MDCs found in NGC 6334
- Short Name:
- J/A+A/602/A77
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To constrain models of high-mass star formation, the Herschel-HOBYS key program aims at discovering massive dense cores (MDCs) able to host the high-mass analogs of low-mass prestellar cores, which have been searched for over the past decade. We here focus on NGC 6334, one of the best-studied HOBYS molecular cloud complexes. We used Herschel/PACS and SPIRE 70-500{mu}m images of the NGC 6334 complex complemented with (sub)millimeter and mid-infrared data. We built a complete procedure to extract ~0.1pc dense cores with the getsources software, which simultaneously measures their far-infrared to millimeter fluxes. We carefully estimated the temperatures and masses of these dense cores from their spectral energy distributions (SEDs). We also identified the densest pc-scale cloud structures of NGC 6334, one 2pcx1pc ridge and two 0.8pcx0.8pc hubs, with volume-averaged densities of ~10^5^cm^-3^. A cross-correlation with high-mass star formation signposts suggests a mass threshold of 75M_{sun}_ for MDCs in NGC 6334. MDCs have temperatures of 9.5-40K, masses of 75-1000M_{sun}_, and densities of 1x10^5^-7x10^7^cm^-3^. Their mid-infrared emission is used to separate 6 IR-bright and 10 IR-quiet protostellar MDCs while their 70{mu}m emission strength, with respect to fitted SEDs, helps identify 16 starless MDC candidates. The ability of the latter to host high-mass prestellar cores is investigated here and remains questionable. An increase in mass and density from the starless to the IR-quiet and IR-bright phases suggests that the protostars and MDCs simultaneously grow in mass. The statistical lifetimes of the high-mass prestellar and protostellar core phases, estimated to be 1-7x10^4^yr and at most 3x10^5^yr respectively, suggest a dynamical scenario of high-mass star formation. The present study provides good mass estimates for a statistically significant sample, covering the earliest phases of high-mass star formation. High-mass prestellar cores may not exist in NGC 6334, favoring a scenario presented here, which simultaneously forms clouds, ridges, MDCs, and high-mass protostars.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/209/25
- Title:
- H_2_O + CH_3_OH maser survey of Orion protostars
- Short Name:
- J/ApJS/209/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of a maser survey toward 99 protostars in the Orion molecular cloud complex are presented. The target sources are low-mass protostars identified from infrared observations. Single-dish observations were carried out in the water maser line at 22GHz and the methanol class I maser lines at 44, 95, and 133GHz. Most of the detected sources were mapped to determine the source positions. Five water maser sources were detected, and they are excited by HH 1-2 VLA 3, HH 1-2 VLA 1, L1641N MM1/3, NGC 2071 IRS 1/3, and an object in the OMC 3 region. The water masers showed significant variability in intensity and velocity with time scales of 1 month or shorter. Four methanol emission sources were detected, and those in the OMC 2 FIR 3/4 and L1641N MM1/3 regions are probably masers. The methanol emission from the other two sources in the NGC 2071 IRS 1-3 and V380 Ori NE regions are probably thermal. For the water masers, the number of detections per protostar in the survey region is about 2%, which suggests that the water masers of low-mass protostars are rarely detectable. The methanol class I maser of low-mass protostars is an even rarer phenomenon, with a detection rate much smaller than 1%.
6443. Hogg 16 peculiar stars
- ID:
- ivo://CDS.VizieR/J/other/NewA/58.1
- Title:
- Hogg 16 peculiar stars
- Short Name:
- J/other/NewA/58.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The study of chemically peculiar (CP) stars in open clusters provides valuable information about their evolutionary status. Their detection can be performed using the Delta-a photometric system, which maps a characteristic flux depression at lambda 5200{AA}. This paper aims at studying the occurrence of CP stars in the earliest stages of evolution of a stellar population by applying this technique to Hogg 16, a very young Galactic open cluster (about 25Myr). We identified several peculiar candidates: two B-type stars with a negative Delta-a index (CD-60 4701, CPD-60 4706) are likely emission-line (Be) stars, even though spectral measurements are necessary for a proper classification of the second one; a third object (CD-60 4703), identified as a Be candidate in literature, appears to be a background B-type supergiant with no significant Delta-a index, which does not rule out the possibility that it is indeed peculiar as the normality line of Delta-a for supergiants has not been studied in detail yet. A fourth object (CD-60 4699) appears to be a magnetic CP star of 8 Msun, but obtained spectral data seem to rule out this hypothesis. Three more magnetic CP star candidates are found in the domain of early F-type stars. One is a probable nonmember and close to the border of significance, but the other two are probably pre-main sequence cluster objects. This is very promising, as it can lead to very strong constraints to the diffusion theory. Finally, we derived the fundamental parameters of Hogg 16 and provide for the first time an estimate of its metal content.
- ID:
- ivo://CDS.VizieR/J/A+A/595/A80
- Title:
- H_2_O lines reduced spectra in 11 ULIRGs or HyLIRGs
- Short Name:
- J/A+A/595/A80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report rest-frame submillimeter H_2_O emission line observations of 11 ultra- or hyper-luminous infrared galaxies (ULIRGs or HyLIRGs) at z~2-4 selected among the brightest lensed galaxies discovered in the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS). Using the IRAM NOrthern Extended Millimeter Array (NOEMA), we have detected 14 new H_2_O emission lines. These include five 3_21_-3_12_ ortho-H_2_O lines (Eup/k=305K) and nine J=2 para-H_2_O lines, either 2_02_-1_11_ (E_up/k=101K) or 2_11_-2_02_ (E_up/k = 137K). The apparent luminosities of the H_2_O emission lines are {mu}L_H2O_~6-21x10^8^L_{sun}_ (3<{mu}<15, where {mu} is the lens magnification factor), with velocity-integrated line fluxes ranging from 4-15Jy.km/s. We have also observed CO emission lines using EMIR on the IRAM 30m telescope in seven sources (most of those have not yet had their CO emission lines observed). The velocity widths for CO and H_2_O lines are found to be similar, generally within 1{sigma} errors in the same source. With almost comparable integrated flux densities to those of the high-J CO line (ratios range from 0.4 to 1.1), H_2_O is found to be among the strongest molecular emitters in high-redshift Hy/ULIRGs. We also confirm our previously found correlation between luminosity of H_2_O (LH_2_O) and infrared (LIR) that LH_2_O~LIR^(1.1-1.2)^, with our new detections. This correlation could be explained by a dominant role of far-infrared pumping in the H_2_O excitation. Modelling reveals that the far-infrared radiation fields have warm dust temperature T_warm_~45-75K, H_2_O column density per unit velocity interval N_H2O_/{DELTA}V>~0.3x10^15^km/s/cm^2^ and 100{mu}m continuum opacity {tau}_100_>1 (optically thick), indicating that H_2_O is likely to trace highly obscured warm dense gas. However, further observations of J>=4 H_2_O lines are needed to better constrain the continuum optical depth and other physical conditions of the molecular gas and dust. We have also detected H_2_O^+^ emission in three sources. A tight correlation between L_H_2_O and L_H_2_O^+^ has been found in galaxies from low to high redshift. The velocity-integrated flux density ratio between H_2_O^+^ and H_2_O suggests that cosmic rays generated by strong star formation are possibly driving the H_2_O^+^ formation.
6445. H2O maser classification
- ID:
- ivo://CDS.VizieR/J/ApJ/658/1096
- Title:
- H2O maser classification
- Short Name:
- J/ApJ/658/1096
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of 22GHz H2O maser observations of a sample of 85 post-asymptotic giant branch (post-AGB) candidate stars, selected on the basis of their OH 1612MHz maser and far-infrared properties. All sources were observed with the Tidbinbilla 70m radio telescope, and 21 detections were made; 86GHz SiO Mopra observations of a subset of the sample are also presented.
- ID:
- ivo://CDS.VizieR/J/ApJ/669/424
- Title:
- H2O maser emissions of IRAS 19134+2131
- Short Name:
- J/ApJ/669/424
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the Very Long Baseline Array at six epochs, we have observed H_2_O maser emission in the preplanetary nebula IRAS 19134+2131 (I19134), in which the H_2_O maser spectrum has two groups of emission features separated in radial velocity by ~100km/s. We also obtained optical images of I19134 with the Hubble Space Telescope to locate the bipolar reflection nebula in this source for the first time.
- ID:
- ivo://CDS.VizieR/J/MNRAS/430/1309
- Title:
- H_2_O masers in AFGL 2591 VLA 3-N
- Short Name:
- J/MNRAS/430/1309
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we analyse multi-epoch very long baseline interferometry water maser observations carried out with the Very Long Baseline Array towards the high-mass star-forming region AFGL 2591. We detected maser emission associated with the radio continuum sources VLA 2 and VLA 3. In addition, a water maser cluster, VLA 3-N, was detected ~0.5arcsec north of VLA 3. We concentrate the discussion of this paper on the spatio-kinematical distribution of the water masers towards VLA 3-N. The water maser emission towards the region VLA 3-N shows two bow-shock-like structures, northern and southern, separated from each other by ~100mas (~330AU). The spatial distribution and kinematics of the water masers in this cluster have persisted over a time span of 7yr. The northern bow shock has a somewhat irregular morphology, while the southern one has a remarkably smooth morphology. We measured the proper motions of 33 water maser features, which have an average proper motion velocity of ~1.3mas/yr (~20km/s). The morphology and the proper motions of this cluster of water masers show systematic expanding motions that could imply one or two different centres of star formation activity. We made a detailed model for the southern structure, proposing two different kinematic models to explain the three-dimensional spatio-kinematical distribution of the water masers: (1) a static central source driving the two bow-shock structures and (2) two independent driving sources, one of them exciting the northern bow-shock structure, and the other one, a young runaway star moving in the local molecular medium exciting and moulding the remarkably smoother southern bow-shock structure. Future observations will be necessary to discriminate between the two scenarios, in particular by identifying the still unseen driving source(s).
- ID:
- ivo://CDS.VizieR/J/A+A/291/261
- Title:
- H2O masers in HII regions
- Short Name:
- J/A+A/291/261
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of a survey of 22.2GHz H2O maser emission towards a large sample of HII regions (427) detected in hydrogen recombination lines (Lockman) are presented. The sample favours classical HII regions with large excitation parameter. We found 68 water maser sources, 17 of which are new detections. Adding the detections found in the literature, the total number of masers associated with the sample is 80. The overall maser percentage is low (19%), much less than what found in samples of ultracompact (UC) HII regions. The percentage changes if we divide our sample into two sub-classes: HII regions known to have ultracompact components (i.e. where a younger generation of star formation is also present) and the rest. In the first sub-class the maser percentage is 28%, in the second 15%. The total number of masers in HII regions where no UC component has been (so far) reported is 43. This value is greater than that expected from the ratio between the lifetime of the HII region (10^6^yr) and that of the maser phase, even assuming a maser lifetime as long as 10^5^yr. This implies that maser excitation (and star formation) occurs several times in the lifetime of the same star forming complex. From 410 positions observed, 230 can be associated with a high degree of confidence to an IRAS Point Source. We expect that most of the HII regions not associated with IRAS PS are diffuse regions in the last phases of their evolution. The percentage of water masers in this sub-class is very low: 8%. The number of masers with no counterpart in the Lockman sample (and above Dec=-30{deg}) is very large: 334. This number most probably reflects the extreme high density conditions known to exist in the earliest phases of an HII region, which strongly reduce its radio continuum and line emission. The analysis of a homogeneous sample of classical HII regions allows to confirm in a quantitative fashion the well known result that the maser phenomenon occurs during the earliest phase of the evolution of a massive star and that it fades away as the HII region evolves into the diffuse stage.
- ID:
- ivo://CDS.VizieR/J/ApJS/155/577
- Title:
- H2O masers in W49 North and Sagittarius B2
- Short Name:
- J/ApJS/155/577
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the Very Large Array (VLA) of the National Radio Astronomy Observatory in the A and B configurations, we have obtained simultaneous high-resolution observations of both the 22GHz H2O maser lines as well as the 22GHz continuum for the H II regions W49N and Sagittarius B2.
- ID:
- ivo://CDS.VizieR/J/A+AS/127/181
- Title:
- H2O maser sources new detections
- Short Name:
- J/A+AS/127/181
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observations of H_2_O maser sources on the 13.7m radio telescope of Purple Mountain Observatory from 1990 Aug. to 1994 Jan. are summarized. For searching new water masers, the total number of search candidates is about 360, with 110 objects detected. Among them are 96 new detections. A list of the new detections and their spectra are presented.