- 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.
Number of results to display per page
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/MNRAS/456/2041
- Title:
- Fragmentation in filamentary molecular clouds
- Short Name:
- J/MNRAS/456/2041
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent surveys of dust continuum emission at sub-mm wavelengths have shown that filamentary molecular clouds are ubiquitous along the Galactic plane. These structures are inhomogeneous, with overdensities that are sometimes associated with infrared emission and active of star formation. To investigate the connection between filaments and star formation, requires an understanding of the processes that lead to the fragmentation of filaments and a determination of the physical properties of the overdensities (clumps). In this paper, we present a multiwavelength study of five filamentary molecular clouds, containing several clumps in different evolutionary stages of star formation. We analyse the fragmentation of the filaments and derive the physical properties of their clumps. We find that the clumps in all filaments have a characteristic spacing consistent with the prediction of the 'sausage' instability theory, regardless of the complex morphology of the filaments or their evolutionary stage. We also find that most clumps have sufficient mass and density to form high-mass stars, supporting the idea that high-mass stars and clusters form within filaments.
- ID:
- ivo://CDS.VizieR/J/A+A/627/A94
- Title:
- FS Tau B two epoch spectro-imagery
- Short Name:
- J/A+A/627/A94
- Date:
- 23 Mar 2022 16:28:17
- Publisher:
- CDS
- Description:
- Herbig-Haro (HH) flows exhibit a large variety of morphological and kinematical structures such as bow shocks, Mach disks, and deflection shocks. Both proper motion (PM) and radial velocity investigations are essential to understand the physical nature of such structures. We investigate the kinematics and PM of spectrally separated structures in the FS Tau B HH flow. Collating these data makes it possible to understand the origin of these structures and to explain the unusual behavior of the jet. On the other hand, the study of emission profiles in the associated reflection nebulae allows us to consider the source of the outflow both from edge-on and pole-on points of view. We present the observational results obtained with the 6 m telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences using the SCORPIO multimode focal reducer with a scanning Fabry-Perot interferometer. Two epochs of the observations of the FS Tau B region in H{alpha} emission (2001 and 2012) allowed us to measure the PM of the spectrally separated inner structures of the jet. In addition to already known emission structures in the FS Tau B system, we discover new features in the extended part of the jet and in the counter-jet. Moreover, we reveal a new HH knot in the HH 276 independent outflow system and point out its presumable source. In the terminal working surface of the jet, structures with different radial velocities have PMs of the same value. This result can be interpreted as the direct observation of bow-shock and Mach disk regions. A bar-like structure, located southwest from the source demonstrates zero PM and can be considered as one more example of deflection shock. An analysis of H{alpha} profiles in the reflection nebulae R1 and R3 indicates the uniqueness of this object, which can be studied in pole-on and edge-on directions simultaneously.
- ID:
- ivo://CDS.VizieR/J/ApJS/160/220
- Title:
- Full-polarization observations of OH masers
- Short Name:
- J/ApJS/160/220
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present full-polarization VLBA maps of the ground-state, main-line, ^2^{Pi}_3/2_, J=3/2 OH masers in 18 Galactic massive star-forming regions. This is the first large polarization survey of interstellar hydroxyl masers at VLBI resolution. A total of 184 Zeeman pairs are identified, and the corresponding magnetic field strengths are indicated. We also present spectra of the NH_3_ emission or absorption in these star-forming regions.
- ID:
- ivo://CDS.VizieR/J/ApJ/764/25
- Title:
- FUSE spectra analysis of hot subdwarf stars
- Short Name:
- J/ApJ/764/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- When the neutral interstellar medium is exposed to extreme-ultraviolet and soft X-ray radiation, the argon atoms in it are far more susceptible to being ionized than the hydrogen atoms. We make use of this fact to determine the level of ionization in the nearby warm neutral medium. By analyzing Far-Ultraviolet Spectroscopic Explorer observations of ultraviolet spectra of 44 hot subdwarf stars a few hundred parsecs away from the Sun, we can compare column densities of Ar I to those of O I, where the relative ionization of oxygen can be used as a proxy for that of hydrogen. The measured deficiency [ArI/OI]=-0.427+/-0.11dex below the expectation for a fully neutral medium implies that the electron density n(e){approx}0.04/cm3 if n(H)=0.5/cm3. This amount of ionization is considerably larger than what we expect from primary photoionizations resulting from cosmic rays, the diffuse X-ray background, and X-ray emitting sources within the medium, along with the additional ionizations caused by energetic secondary photoelectrons, Auger electrons, and photons from helium recombinations. We favor an explanation that bursts of radiation created by previous, nearby supernova remnants that have faded by now may have elevated the ionization, and the gas has not yet recombined to a quiescent level. A different alternative is that the low-energy portion of the soft X-ray background is poorly shielded by the H I because it is frothy and has internal pockets of very hot, X-ray emitting gases.
- ID:
- ivo://CDS.VizieR/J/ApJ/647/328
- Title:
- FUSE survey of OVI in ISM
- Short Name:
- J/ApJ/647/328
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a survey of diffuse OVI emission in the interstellar medium (ISM) obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). Spanning 5.5yr of FUSE observations, from launch through 2004 December, our data set consists of 2925 exposures along 183 sight lines, including all of those with previously published OVI detections. The data were processed using an implementation of CalFUSE version 3.1 modified to optimize the signal-to-noise ratio and velocity scale of spectra from an aperture-filling source.
- ID:
- ivo://CDS.VizieR/J/ApJS/176/59
- Title:
- FUSE survey of OVI in the disk of the Milky Way
- Short Name:
- J/ApJS/176/59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To probe the distribution and physical characteristics of interstellar gas at temperatures T~3x10^5^K in the disk of the Milky Way, we have used the Far Ultraviolet Spectroscopic Explorer (FUSE) to observe absorption lines of OVI{lambda}1032 toward 148 early-type stars situated at distances >1kpc. After subtracting off a mild excess of OVI arising from the Local Bubble, combining our new results with earlier surveys of OVI, and eliminating stars that show conspicuous localized X-ray emission, we find an average OVI midplane density n_0_=1.3x10^-8^cm^-3^. The density decreases away from the plane of the Galaxy in a way that is consistent with an exponential scale height of 3.2kpc at negative latitudes or 4.6kpc at positive latitudes.
- ID:
- ivo://CDS.VizieR/J/ApJ/647/312
- Title:
- FUSE survey of OVI in the Milky Way
- Short Name:
- J/ApJ/647/312
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a survey of OVI {lambda}1032 emission in the Milky Way using data from the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. The observations span the period from launch in 1999 to 2003 July. Our survey contains 112 sight lines, 23 of which show measurable OVI {lambda}1032 emission. The OVI {lambda}1032 emission feature was detected at all latitudes and exhibits intensities of 1900-8600photons/s/cm^2^/sr. Combined with values from the literature, these emission measurements are consistent with the picture derived from recent OVI absorption surveys: high-latitude sight lines probe OVI-emitting gas in a clumpy, thick disk or halo, while low-latitude sight lines sample mixing layers and interfaces in the thin disk of the Galaxy.
- ID:
- ivo://CDS.VizieR/J/A+A/650/A142
- Title:
- G24.78+0.08 A1 ALMA images and datacubes
- Short Name:
- J/A+A/650/A142
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Hyper-compact (HC) or ultra-compact HII regions are the first manifestations of the radiation feedback from a newly born massive star. Therefore, their study is fundamental to understanding the process of massive (>=8M_{sun}_) star formation. We employed Atacama Large Millimeter/submillimeter Array (ALMA) 1.4mm Cycle 6 observations to investigate at high angular resolution (~0.050, corresponding to 330au) the HC HII region inside molecular core A1 of the high-mass star-forming cluster G24.78+0.08. We used the H30{alpha} emission and different molecular lines of CH_3_CN and ^13^CH_3_CN to study the kinematics of the ionized and molecular gas, respectively. At the center of the HC HII region, at radii <~500au, we observe two mutually perpendicular velocity gradients, which are directed along the axes at PA=39{deg} and PA=133{deg}, respectively. The velocity gradient directed along the axis at PA=39{deg} has an amplitude of 22km/s/mpc, which is much larger than the other;s, 3km/s/mpc. We interpret these velocity gradients as rotation around, and expansion along, the axis at PA=39{deg}. We propose a scenario where the H30{alpha} line traces the ionized heart of a disk-jet system that drives the formation of the massive star (~20M_{sun}_) responsible for the HC HII region. Such a scenario is also supported by the position-velocity plots of the CH_3_CN and ^13^CH_3_CN lines along the axis at PA=133{deg}, which are consistent with Keplerian rotation around a 20M_{sun}_ star. Toward the HC HII region in G24.78+0.08, the coexistence of mass infall (at radii of ~5000au), an outer molecular disk (from <~4000 au to >~500au), and an inner ionized disk (<~500au) indicates that the massive ionizing star is still actively accreting from its parental molecular core. To our knowledge, this is the first example of a molecular disk around a high-mass forming star that, while becoming internally ionized after the onset of the HII region, continues to accrete mass onto the ionizing star.
