- ID:
- ivo://CDS.VizieR/J/A+A/558/A58
- Title:
- NGC 1333-IRAS 4A C^18^O, NO and O_2_ spectra
- Short Name:
- J/A+A/558/A58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- According to traditional gas-phase chemical models, O_2_ should be abundant in molecular clouds, but until recently, attempts to detect interstellar O_2_ line emission with ground- and space-based observatories have failed. Following the multi-line detections of O_2_ with low abundances in the Orion and rho Oph A molecular clouds with Herschel, it is important to investigate other environments, and we here quantify the O_2_ abundance near a solar-mass protostar. Observations of molecular oxygen, O_2_, at 487GHz toward a deeply embedded low-mass Class 0 protostar, NGC 1333-IRAS 4A, are presented, using the Heterodyne Instrument for the Far Infrared (HIFI) on the Herschel Space Observatory. Complementary data of the chemically related NO and CO molecules are obtained as well. The high spectral resolution data are analysed using radiative transfer models to infer column densities and abundances, and are tested directly against full gas-grain chemical models. The deep HIFI spectrum fails to show O_2_ at the velocity of the dense protostellar envelope, implying one of the lowest abundance upper limits of O_2_/H_2_ at <6x10^-3^ (3 sigma). The O_2_/CO abundance ratio is less than 0.005. However, a tentative (4.5 sigma) detection of O_2_ is seen at the velocity of the surrounding NGC1333 molecular cloud, shifted by 1km/s relative to the protostar. For the protostellar envelope, pure gas-phase models and gas-grain chemical models require a long pre-collapse phase (~0.7-1x10^6^-years), during which atomic and molecular oxygen are frozen out onto dust grains and fully converted to H_2_O, to avoid overproduction of O_2_ in the dense envelope. The same model also reproduces the limits on the chemically related NO molecule if hydrogenation of NO on the grains to more complex molecules such as NH_2_OH, found in recent laboratory experiments, is included. The tentative detection of O_2_ in the surrounding cloud is consistent with a low-density PDR model with small changes in reaction rates. The low O_2_ abundance in the collapsing envelope around a low-mass protostar suggests that the gas and ice entering protoplanetary disks is very poor in O_2_.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/613/A29
- Title:
- NGC1333-IRAS2A water snowline imaging
- Short Name:
- J/A+A/613/A29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Snowlines are key ingredients for planet formation. Providing observational constraints on the locations of the major snowlines is therefore crucial for fully connecting planet compositions to their formation mechanism. Unfortunately, the most important snowline, that of water, is very difficult to observe directly in protoplanetary disks due to its close proximity to the central star. Based on chemical considerations, HCO^+^ is predicted to be a good chemical tracer of the water snowline, because it is particularly abundant in dense clouds when water is frozen out. This work aims to map the optically thin isotopologue H^13^CO^+^ toward the envelope of the low-mass protostar NGC1333-IRAS2A, where the snowline is at larger distance from the star than in disks. Comparison with previous observations of H_2_^18^O will show whether H^13^CO^+^ is indeed a good tracer of the water snowline. NGC1333-IRAS2A was observed using NOEMA at ~0.9 arcsec resolution, targeting the H^13^CO^+^ J=3-2 transition at 260.255GHz. The integrated emission profile was analyzed using 1D radiative transfer modeling of a spherical envelope with a parametrized abundance profile for H^13^CO^+^. This profile was validated with a full chemical model. The H^13^CO^+^ emission peaks ~2-arcsec northeast of the continuum peak, whereas H_2_^18^O shows compact emission on source. Quantitative modeling shows that a decrease in H13CO+ abundance by at least a factor of six is needed in the inner ~360AU to reproduce the observed emission profile. Chemical modeling predicts indeed a steep increase in HCO^+^ just outside the water snowline; the 50% decrease in gaseous H_2_O at the snowline is not enough to allow HCO^+^ to be abundant. This places the water snowline at 225AU, further away from the star than expected based on the 1D envelope temperature structure for NGC1333-IRAS2A. In contrast, DCO^+^ observations show that the CO snowline is at the expected location, making an outburst scenario unlikely. The spatial anticorrelation of the H^13^CO^+^ and H_2_^18^O emission provide a proof of concept that H^13^CO^+^ can be used as a tracer of the water snowline.
- ID:
- ivo://CDS.VizieR/J/A+A/543/A88
- Title:
- NGC7538IRS1 and NGC7538S 1.36mm maps
- Short Name:
- J/A+A/543/A88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The nature of embedded accretion disks around forming high-mass stars is one of the missing puzzle pieces for a general understanding of the formation of the most massive and luminous stars. We want to dissect the small-scale structure of the dust continuum and kinematic gas emission toward two of the most prominent high-mass disk candidates.
- ID:
- ivo://CDS.VizieR/J/A+A/558/A81
- Title:
- NGC 7538 IRS1 maps in CH3OH, HCN and HCO+
- Short Name:
- J/A+A/558/A81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Revealing the fragmentation, infall, and outflow processes in the immediate environment around massive young stellar objects is crucial for understanding the formation of the most massive stars. With this goal in mind we present the so far highest spatial-resolution thermal submm line and continuum observations toward the young high-mass protostar NGC 7538 IRS1. Using the Plateau de Bure Interferometer in its most extended configuration at 843um wavelength, we achieved a spatial resolution of 0.2"x0.17", corresponding to ~500AU at a distance of 2.7kpc.
- ID:
- ivo://CDS.VizieR/J/A+A/605/A61
- Title:
- NGC 7538 IRS1 VLA maps in CH_3_OH and NH_3_
- Short Name:
- J/A+A/605/A61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High-mass stars have a high degree of multiplicity and most likely form via disk accretion processes. The detailed physics of the binary and disk formation are still poorly constrained. We seek to resolve the central substructures of the prototypical high-mass star-forming region NGC7538IRS1 at the highest possible spatial resolution line and continuum emission to investigate the protostellar environment and kinematics. Using the Karl G. Jansky Very Large Array (VLA) in its most extended configuration at ~24GHz has allowed us to study the NH_3_ and thermal CH_3_OH emission and absorption as well as the cm continuum emission at an unprecedented spatial resolution of 0.06"x0.05", corresponding to a linear resolution of ~150AU at a distance of 2.7kpc.
- ID:
- ivo://CDS.VizieR/J/A+A/647/A154
- Title:
- NGC6357 686 molecular cores physical properties
- Short Name:
- J/A+A/647/A154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We mapped the NGC6357 star forming region at 450 and 850 micron with SCUBA-2 and in the CO(3-2) line with HARP at the JCMT. We also retrieved Herschel Hi-GAL data at 70 and 160 micron. The submm continuum emission was decomposed into cores with the algorithm Gaussclumps (Stutzki & Guesten, 1990ApJ...356..513S). By fitting greybodies to the core 4-point SEDs we derived their temperature and mass. Core mass functions were derived in the region more exposed to the FUV flux from massive stars (associated with the HII regions G353.2+0.9, G353.1+0.6, and G353.2+0.7) and in the region less exposed. Table 2 lists the physical properties of the cores in NGC6357.
- ID:
- ivo://CDS.VizieR/J/A+A/527/A77
- Title:
- NGC 1893 optical and NIR photometry
- Short Name:
- J/A+A/527/A77
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Different environmental conditions can play a crucial role in determining final products of the star formation process and in this context, less favorable activities of star formation are expected in the external regions of our Galaxy. We studied the properties of the young open cluster NGC 1893 located about 12kpc from the galactic center, to investigate how different physical conditions can affect the process of star formation. By adopting a multiwavelength approach, we compiled a catalog extending from X-rays to NIR data to derive the cluster membership. In addition, optical and NIR photometric properties are used to evaluate the cluster parameters. We find 415 diskless candidate members plus 1061 young stellar objects with a circumstellar disk or class II candidate members, 125 of which are also H{alpha} emitters. Considering the diskless candidate members, we find that the cluster distance is 3.6+/-0.2kpc and the mean interstellar reddening is E(B-V)=0.6+/-0.1 with evidence of differential reddening in the whole surveyed region. NGC 1893 contains a conspicuous population of pre-main sequence stars together with the well studied main sequence cluster population; we found a disk fraction of about 70% similar to that found in clusters of similar age in the solar neighbor and then, despite expected unfavorable conditions for star formation, we conclude that very rich young clusters can form also in the outer regions of our Galaxy.
- ID:
- ivo://CDS.VizieR/J/MNRAS/453/2006
- Title:
- NGC 2264 SCUBA-2 observations
- Short Name:
- J/MNRAS/453/2006
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present wide-field observations of the NGC 2264 molecular cloud in the dust continuum at 850 and 450{mu}m using SCUBA-2 on the James Clerk Maxwell Telescope. Using ^12^CO 3->2 molecular line data, we determine that emission from CO contaminates the 850{mu}m emission at levels ~30 per cent in localized regions associated with high-velocity molecular outflows. Much higher contamination levels of 60 per cent are seen in shocked regions near the massive star S Mon. If not removed, the levels of CO contamination would contribute an extra 13 per cent to the dust mass in NGC 2264. We use the fellwalker routine to decompose the dust into clumpy structures, and a Hessian-based routine to decompose the dust into filamentary structures. The filaments can be described as a hub-filament structure, with lower column density filaments radiating from the NGC 2264 C protocluster hub. Above mean filament column densities of 2.4x10^22^cm^-2^, star formation proceeds with the formation of two or more protostars. Below these column densities, filaments are starless, or contain only a single protostar.
- ID:
- ivo://CDS.VizieR/J/A+A/615/A18
- Title:
- NIKA view of two star-forming IRDCs
- Short Name:
- J/A+A/615/A18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The thermal emission of dust grains is a powerful tool for probing cold, dense regions of molecular gas in the interstellar medium, and so constraining dust properties is key to obtaining accurate measurements of dust mass and temperature. By placing constraints on the dust emissivity spectral index, {beta}, towards two star-forming infrared dark clouds - SDC18.888-0.476 and SDC24.489-0.689 - we aim to evaluate the role of mass concentration in the associated star-formation activity. We exploited the simultaneous 1.2mm and 2.0mm imaging capability of the NIKA camera on the IRAM 30m telescope to construct maps of {beta} for both clouds, and by incorporating Herschel observations, we created H_2_ column density maps with 13" angular resolution. While we find no significant systematic radial variations around the most massive clumps in either cloud on 0.1 pc scales, their mean {beta} values are significantly different, with {bar}{beta}=2.07+/-0.09(random)+/-0.25(systematic) for SDC18.888-0.476 and {bar}{beta}=1.71+/-0.09(random)+/-0.25(systematic) for SDC24.489-0.689. These differences could be a consequence of the very different environments in which both clouds lie, and we suggest that the proximity of SDC18.888-0.476 to the W39 HII region may raise {beta} on scales of ~1pc. We also find that the mass in SDC24.489-0.689 is more centrally concentrated and circularly symmetric than in SDC18.888-0.476, and is consistent with a scenario in which spherical globally-collapsing clouds concentrate a higher fraction of their mass into a single core than elongated clouds that will more easily fragment, distributing their mass into many cores. We demonstrate that {beta} variations towards interstellar clouds can be robustly constrained with high signal-to-noise ratio (S/N) NIKA observations, providing more accurate estimates of their masses. The methods presented here will be applied to the Galactic Star Formation with NIKA2 (GASTON) guaranteed time large programme, extending our analysis to a statistically significant sample of star-forming clouds.
- ID:
- ivo://CDS.VizieR/J/A+A/646/A122
- Title:
- NOEMA millimeter reduced data cubes of HerBS-89a
- Short Name:
- J/A+A/646/A122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Exploiting the sensitivity of the IRAM NOrthern Extended Millimeter Array (NOEMA) and its ability to process large instantaneous bandwidths, we have studied the morphology and other properties of the molecular gas and dust in the starburst galaxy, H-ATLAS J131611.5+281219 (HerBS- 89a), at z=2.95. High angular resolution (0.3") images reveal a partial 1.0" diameter Einstein ring in the dust continuum emission and the molecular emission lines of ^12^CO(9-8) and H_2_O(2_02_-1_11_). Together with lower angular resolution (0.6") images, we report the detection of a series of molecular lines including the three fundamental transitions of the molecular ion OH+, namely (1_1_-0_1_), (1_2_-0_1_) and (1_0_-0_1_), seen in absorption; the molecular ion CH+(1-0) seen in absorption (and tentatively in emission); two transitions of amidogen (NH_2_), namely (2_02_-1_11_) and (2_20_-2_11_) seen in emission; and HCN(1_1_-1_0_) and/or NH(1_2_-0_1_) seen in absorption. The NOEMA data are complemented with Very Large Array data tracing the ^12^CO(1-0) emission line, which provides a measurement of the total mass of molecular gas and an anchor for a CO excitation analysis. In addition, we present Hubble Space Telescope imaging that reveals the foreground lensing galaxy in the near-infrared (1.15um). Together with photometric data from the Gran Telescopio Canarias, we derive a photometric redshift of zphot=0.9^+0.3^_-0.5_ for the foreground lensing galaxy. Modelling the lensing of HerBS-89a, we reconstruct the dust continuum (magnified by a factor {mu}~=5.0) and molecular emission lines (magnified by {mu}~4-5) in the source plane, which probe scales of ~0.1" (or 800pc). The ^12^CO(9-8) and H_2_O(2_02_-1_11_) emission lines have comparable spatial and kinematic distributions; the source-plane reconstructions do not clearly distinguish between a one-component and a two-component scenario, but the latter, which reveals two compact rotating components with sizes of ~=1kpc, that are likely merging, more naturally accounts for the broad line widths observed in HerBS-89a. In the core of HerBS-89a, very dense gas with n_H2_~10^7-9^cm^-3^ is revealed by the NH_2_ emission lines and the possible HCN(1_1_-1_0_) absorption line. HerBS-89a is a powerful star forming galaxy with a molecular gas mass of M_mol_=(2.1+/-0.4)x10^11^M_{sun}_, an infrared luminosity of L_IR_=(4.6+/-0.4)x10^12^L_{sun}_, and a dust mass of M_dust_=(2.6+/-0.2)x10^9^M_{sun}_, yielding a dust-to-gas ratio {delta}_GDR_~=80. We derive a star formation rate SFR=614+/-59M_{sun}_/yr and a depletion timescale {tau}_depl_=(3.4+/-1.0)x10^8^years. The OH+ and CH+ absorption lines, which trace low (~100cm^-3^) density molecular gas, all have their main velocity component red-shifted by {DELTA}V~100km/s relative to the global CO reservoir. We argue that these absorption lines trace a rare example of gas inflow towards the center of a starburst galaxy, indicating that HerBS-89a is accreting gas from its surroundings.