- ID:
- ivo://CDS.VizieR/J/ApJ/717/L133
- Title:
- Formaldehyde maser flares in IRAS 18566+0408
- Short Name:
- J/ApJ/717/L133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report results of an extensive observational campaign of the 6cm formaldehyde maser in the young massive stellar object IRAS 18566+0408 (G37.55+0.20) conducted from 2002 to 2009. Using the Arecibo Telescope, the Very Large Array, and the Green Bank Telescope, we discovered quasi-periodic formaldehyde flares (P~237 days). Based on Arecibo observations, we also discovered correlated variability between formaldehyde (H_2_CO) and methanol (CH_3_OH) masers. The H_2_CO and CH_3_OH masers are not spatially coincident, as demonstrated by different line velocities and high angular resolution MERLIN observations. The flares could be caused by variations in the infrared radiation field, possibly modulated by periodic accretion onto a young binary system.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/449/2438
- Title:
- Formamide detection with ASAI-IRAM
- Short Name:
- J/MNRAS/449/2438
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Formamide (NH_2_CHO) has been proposed as a pre-biotic precursor with a key role in the emergence of life on Earth. While this molecule has been observed in space, most of its detections correspond to high-mass star-forming regions. Motivated by this lack of investigation in the low-mass regime, we searched for formamide, as well as isocyanic acid (HNCO), in 10 low- and intermediate-mass pre-stellar and protostellar objects. The present work is part of the IRAM Large Programme ASAI (Astrochemical Surveys At IRAM), which makes use of unbiased broad-band spectral surveys at millimetre wavelengths. We detected HNCO in all the sources and NH_2_CHO in five of them. We derived their abundances and analysed them together with those reported in the literature for high-mass sources. For those sources with formamide detection, we found a tight and almost linear correlation between HNCO and NH_2_CHO abundances, with their ratio being roughly constant - between 3 and 10 - across 6 orders of magnitude in luminosity. This suggests the two species are chemically related. The sources without formamide detection, which are also the coldest and devoid of hot corinos, fall well off the correlation, displaying a much larger amount of HNCO relative to NH_2_CHO. Our results suggest that, while HNCO can be formed in the gas-phase during the cold stages of star formation, NH_2_CHO forms most efficiently on the mantles of dust grains at these temperatures, where it remains frozen until the temperature rises enough to sublimate the icy grain mantles. We propose hydrogenation of HNCO as a likely formation route leading to NH_2_CHO.
- ID:
- ivo://CDS.VizieR/J/A+A/646/A102
- Title:
- FU Ori multi-band interferometric observations
- Short Name:
- J/A+A/646/A102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- FU Orionis is the archetypal FUor star, a subclass of young stellar object (YSO) that undergo rapid brightening events, often gaining 4-6 magnitudes on timescales of days. This brightening is often associated with a massive increase in accretion; one of the most ubiquitous processes in astrophysics from planets and stars to super-massive black holes. We present multi-band interferometric observations of the FU Ori circumstellar environment, including the first J-band interferometric observations of a YSO. We investigate the morphology and temperature gradient of the inner-most regions of the accretion disk around FU Orionis. We aim to characterise the heating mechanisms of the disk and comment on potential outburst triggering processes. Methods. Recent upgrades to the MIRC-X instrument at the CHARA array allowed the first dual-band J and H observations of YSOs. Using baselines up to 331m, we present high angular resolution data of a YSO covering the near-infrared bands J, H, and K. The unprecedented spectral range of the data allows us to apply temperature gradient models to the innermost regions of FU Ori. We spatially resolve the innermost astronomical unit of the disk and determine the exponent of the temperature gradient of the inner disk to T{prop.to}r^-0.74+/-0.02^. This agrees with theoretical work that predicts T{prop.to}r^-0.75^ for actively accreting, steady state disks, a value only obtainable through viscous heating within the disk. We find a disk which extends down to the stellar surface at 0.015+/-0.007au where the temperature is found to be 5800+/-700K indicating boundary layer accretion. We find a disk inclined at 32+/-4{deg} with a minor-axis position angle of 34+/-11{deg}.
- ID:
- ivo://CDS.VizieR/J/PAZh/39/601
- Title:
- Galactic kinematics from YSOs sample
- Short Name:
- J/PAZh/39/601
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on published sources, we have created a kinematic database on 220 massive (>10M_{sun}_) young Galactic star systems located within <3 kpcof the Sun. Out of them, approximately 100 objects are spectroscopic binary and multiple star systems whose components are massive OB stars; the remaining objects are massive Hipparcos B stars with parallax errors of no more than 10 percent. Based on the entire sample, we have constructed the Galactic rotation curve, determined the circular rotation velocity of the solar neighborhood around the Galactic center R_0_=8kpc, V_0_=259+/-16km/s, and obtained the following spiral density wave parameters: the amplitudes of the radial and azimuthal velocity perturbations f_R_=-10.8+/-1.2km/s, and f_{theta}_=7.9+/-1.3km/s, respectively; the pitch angle for a two-armed spiral pattern i=-6.0+/-0.4deg, with the wavelength of the spiral density wave near the Sun being {lambda}=2.6+/-0.2kpc; and the radial phase of the Sun in the spiral density wave {chi}_{sun}_=-120+/-4{deg}. We show that such peculiarities of the Gould Belt as the local expansion of the system, the velocity ellipsoid vertex deviation, and the significant additional rotation can be explained in terms of the density wave theory. All these effects decrease noticeably once the influence of the spiral density wave on the velocities of nearby stars has been taken into account. The influence of Gould Belt stars on the Galactic parameter estimates has also been revealed. Eliminating them from the kinematic equations has led to the following new values of the spiral density wave parameters: f_{theta}_=2.9+/-2.1km/s and {chi}_{sun}_=-104+/-6{deg}.
- ID:
- ivo://CDS.VizieR/J/ApJ/723/1019
- Title:
- Galactic SFR and gas surface densities
- Short Name:
- J/ApJ/723/1019
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the relation between star formation rate (SFR) and gas surface densities in Galactic star-forming regions using a sample of young stellar objects (YSOs) and massive dense clumps. Our YSO sample consists of objects located in 20 large molecular clouds from the Spitzer cores to disks (c2d; Evans, 2009, Cat. J/ApJS/181/321) and Gould's Belt (GB) survey (L. Allen et al. 2010, in preparation). These data allow us to probe the regime of low-mass star formation, essentially invisible to tracers of high-mass star formation used to establish extragalactic SFR-gas relations. We estimate the gas surface density ({Sigma}_gas_) from extinction (A_V_) maps and YSO SFR surface densities ({Sigma}_SFR_) from the number of YSOs, assuming a mean mass and lifetime. We also divide the clouds into evenly spaced contour levels of A_V_, counting only Class I and Flat spectral energy distribution YSOs, which have not yet migrated from their birthplace. For a sample of massive star-forming clumps, we derive SFRs from the total infrared luminosity and use HCN gas maps to estimate gas surface densities. We find that c2d and GB clouds lie above the extragalactic SFR-gas relations (e.g., Kennicutt-Schmidt law) by factors of up to 17. We use ^12^CO and ^13^CO gas maps of the Perseus and Ophiuchus clouds from the COMPLETE survey (Ridge et al. 2006AJ....131.2921R) to estimate gas surface densities and compare to measurements from A_V_ maps.
- ID:
- ivo://CDS.VizieR/J/ApJS/216/26
- Title:
- GALEX search for T Tauri in Taurus-Auriga
- Short Name:
- J/ApJS/216/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we identify 63 bona fide new candidates to T Tauri stars (TTSs) in the Taurus-Auriga region, using its ultraviolet excess as our baseline. The initial data set was defined from the GALEX all sky survey (AIS). The GALEX satellite obtained images in the near-ultraviolet (NUV) and far-ultraviolet (FUV) bands where TTSs show a prominent excess compared with main-sequence or giants stars. GALEX AIS surveyed the Taurus-Auriga molecular complex, as well as a fraction of the California Nebula and the Perseus complex; bright sources and dark clouds were avoided. The properties of TTSs in the ultraviolet (GALEX), optical (UCAC4), and infrared (2MASS) have been defined using the TTSs observed with the International Ultraviolet Explorer reference sample. The candidates were identified by means of a mixed ultraviolet-optical-infrared excess set of colors; we found that the FUV-NUV versus J-K color-color diagram is ideally suited for this purpose. From an initial sample of 163313 bona fide NUV sources, a final list of 63 new candidates to TTSs in the region was produced. The search procedure has been validated by its ability to detect all known TTSs in the area surveyed: 31 TTSs. Also, we show that the weak-lined TTSs are located in a well-defined stripe in the FUV-NUV versus J-K diagram. Moreover, in this work, we provide a list of TTSs photometric standards for future GALEX-based studies of the young stellar population in star forming regions.
- ID:
- ivo://CDS.VizieR/J/A+A/617/A89
- Title:
- G328.2551-0.5321 ALMA images
- Short Name:
- J/A+A/617/A89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The conditions leading to the formation of the most massive O-type stars, are still an enigma in modern astrophysics. To assess the physical conditions of high-mass protostars in their main accretion phase, here we present a case study of a young massive clump selected from the ATLASGAL survey, G328.2551-0.5321. The source exhibits a bolometric luminosity of 1.3x10^4^L_{sun}_, which allows us to estimate its current protostellar mass to be between ~11 and 16 M_{sun}_. We show high angular-resolution observations with ALMA reaching a physical scale of ~400au. To reveal the structure of this high-mass protostellar envelope in detail at a ~0.17" resolution, we use the thermal dust continuum emission and spectroscopic information, amongst others from the CO (J=3-2) line, which is sensitive to the high velocity molecular outflow, the SiO (J=8-7), and SO_2_ (J=8_2,6_-7_1,7_) lines tracing shocks along the outflow, as well as several CH_3_OH and HC_3_N lines that probe the gas of the inner envelope in the closest vicinity of the protostar. The dust continuum emission reveals a single high-mass protostellar envelope, down to our resolution limit. We find evidence for a compact, marginally resolved continuum source, which is surrounded by azimuthal elongations that could be consistent with a spiral pattern. We also report on the detection of a rotational line of CH_3_OH within its vt=1 torsionally excited state. This shows two bright peaks of emission spatially offset from the dust continuum peak, and exhibiting a distinct velocity component +/-4.5km/s offset compared to the source Vlsr. Rotational diagram analysis and models based on local thermodynamic equilibrium (LTE) assumption require high CH3OH column densities reaching N(CH_3_OH)=1.2-2x10^19^cm^-2^, and kinetic temperatures of the order of 160-200K at the position of these peaks. A comparison of their morphology and kinematics with those of the outflow component of the CO line, and the SO2 line suggests that the high excitation CH3OH spots are associated with the innermost regions of the envelope. While the HC_3_N v7=0 (J=37-36) line is also detected in the outflow, the HC_3_N v7=1e (J=38-37) rotational transition within the molecule's vibrationally excited state shows a compact morphology. We find that the velocity shifts at the position of the observed high excitation CH3OH spots correspond well to the expected Keplerian velocity around a central object with 15M_{sun}_ consistent with the mass estimate based on the source's bolometric luminosity. We propose a picture where the CH_3_OH emission peaks trace the accretion shocks around the centrifugal barrier, pinpointing the interaction region between the collapsing envelope and an accretion disk. The physical properties of the accretion disk inferred from these observations suggest a specific angular momentum several times larger than typically observed towards low-mass protostars. This is consistent with a scenario of global collapse setting on at larger scales that could carry a more significant amount of kinetic energy compared to the core collapse models of low-mass star formation. Furthermore, our results suggest that vibrationally exited HC_3_N emission could be a new tracer for compact accretion disks around high-mass protostars.
- ID:
- ivo://CDS.VizieR/J/ApJS/254/33
- Title:
- Gal. midplane Spitzer/IRAC candidate YSOs (SPICY)
- Short Name:
- J/ApJS/254/33
- Date:
- 19 Jan 2022 09:09:49
- Publisher:
- CDS
- Description:
- We present ~120000 Spitzer/IRAC candidate young stellar objects (YSOs) based on surveys of the Galactic midplane between l~255{deg} and 110{deg}, including the GLIMPSE I, II, and 3D, Vela-Carina, Cygnus X, and SMOG surveys (613 square degrees), augmented by near-infrared catalogs. We employed a classification scheme that uses the flexibility of a tailored statistical learning method and curated YSO data sets to take full advantage of Spitzer's spatial resolution and sensitivity in the mid-infrared ~3-9{mu}m range. Multiwavelength color/magnitude distributions provide intuition about how the classifier separates YSOs from other red IRAC sources and validate that the sample is consistent with expectations for disk/envelope-bearing pre-main-sequence stars. We also identify areas of IRAC color space associated with objects with strong silicate absorption or polycyclic aromatic hydrocarbon emission. Spatial distributions and variability properties help corroborate the youthful nature of our sample. Most of the candidates are in regions with mid-IR nebulosity, associated with star-forming clouds, but others appear distributed in the field. Using Gaia DR2 distance estimates, we find groups of YSO candidates associated with the Local Arm, the Sagittarius-Carina Arm, and the Scutum-Centaurus Arm. Candidate YSOs visible to the Zwicky Transient Facility tend to exhibit higher variability amplitudes than randomly selected field stars of the same magnitude, with many high-amplitude variables having light-curve morphologies characteristic of YSOs. Given that no current or planned instruments will significantly exceed IRAC's spatial resolution while possessing its wide-area mapping capabilities, Spitzer-based catalogs such as ours will remain the main resources for mid-infrared YSOs in the Galactic midplane for the near future.
- ID:
- ivo://CDS.VizieR/J/A+A/608/A133
- Title:
- Gas and dust in star-forming region rho OphA
- Short Name:
- J/A+A/608/A133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate to what degree local physical and chemical conditions are related to the evolutionary status of various objects in star-forming media. rho Oph A displays the entire sequence of low-mass star formation in a small volume of space. Using spectrophotometric line maps of H_2_, H_2_O, NH_3_, N_2_H^+^, O_2_, OI, CO, and CS, we examine the distribution of the atomic and molecular gas in this dense molecular core. The physical parameters of these species are derived, as are their relative abundances in rho Oph A. Using radiative transfer models, we examine the infall status of the cold dense cores from their resolved line profiles of the ground state lines of H_2_O and NH_3_, where for the latter no contamination from the VLA 1623 outflow is observed and line overlap of the hyperfine components is explicitly taken into account. The stratified structure of this photon dominated region (PDR), seen edge-on, is clearly displayed. Polycyclic aromatic hydrocarbons (PAHs) and OI are seen throughout the region around the exciting star S1. At the interface to the molecular core 0.05pc away, atomic hydrogen is rapidly converted into H_2_, whereas OI protrudes further into the molecular core. This provides oxygen atoms for the gas-phase formation of O_2_ in the core SM1, where X(O_2_)~5x10^-8^. There, the ratio of the O_2_ to H_2_O abundance [X(H_2_O)~5x10^-9^] is significantly higher than unity. Away from the core, O_2_ experiences a dramatic decrease due to increasing H_2_O formation. Outside the molecular core, on the far side as seen from S1, the intense radiation from the 0.5pc distant early B-type star HD147889 destroys the molecules. Towards the dark core SM1, the observed abundance ratio X(O_2_)/X(H_2_O)>1, which suggests that this object is extremely young, which would explain why O_2_ is such an elusive molecule outside the solar system.
- ID:
- ivo://CDS.VizieR/J/A+A/578/A131
- Title:
- Gas and dust in the star-forming region rho OphA
- Short Name:
- J/A+A/578/A131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using mapping observations of the very dense rho Oph A core, we examined standard 1D and non-standard 3D methods to analyse data of far-infrared and submillimeter continuum radiation. The resulting dust surface density distribution can be compared to that of the gas. The latter was derived from the analysis of accompanying molecular line emission, observed with Herschel from space and with APEX from the ground. As a gas tracer we used N_2_H^+^, which is believed to be much less sensitive to freeze-out than CO and its isotopologues. Radiative transfer modelling of the N_2_H^+^(J=3-2) and (J=6-5) lines with their hyperfine structure explicitly taken into account provides solutions for the spatial distribution of the column density N(H2), hence the surface density distribution of the gas. The gas-to-dust mass ratio is varying across the map, with very low values in the central regions around the core SM1. The global average, =88, is not far from the canonical value of 100, however. In rho Oph A, the exponent beta of the power-law description for the dust opacity exhibits a clear dependence on time, with high values of 2 for the envelope-dominated emission in starless Class-1 sources to low values close to 0 for the disk-dominated emission in ClassIII objects. beta assumes intermediate values for evolutionary classes in between. Since beta is primarily controlled by grain size, grain growth mostly occurs in circumstellar disks. The spatial segregation of gas and dust, seen in projection toward the core centre, probably implies that, like C^18^O, also N_2_H^+^ is frozen onto the grains.
