- ID:
- ivo://CDS.VizieR/J/MNRAS/466/2614
- Title:
- Complex cluster Abell 1758 stars
- Short Name:
- J/MNRAS/466/2614
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a weak-lensing and dynamical study of the complex cluster Abell 1758 (A1758, {bar}z=0.278) supported by hydrodynamical simulations. This cluster is composed of two main structures called A1758N and A1758S. The northern structure is composed of A1758NW and A1758NE, with lensing determined masses of 7.90_-1.55_^+1.89^x10^14^M_{sun}_ and 5.49_-1.33_^+1.67^x10^14^M_{sun}_, respectively. They show a remarkable feature: while in A1758NW, there is a spatial agreement among weak-lensing mass distribution, intracluster medium and its brightest cluster galaxy (BCG), in A1758NE, the X-ray peak is located 96_-15_^+14^ arcsec away from the mass peak and BCG positions. Given the detachment between gas and mass, we could use the local surface mass density to estimate an upper limit for the dark matter self-interaction cross-section: {sigma}/m<5.83cm^2^/g. Combining our velocity data with hydrodynamical simulations, we have shown that A1758 NW and NE had their closest approach 0.27Gyr ago and their merger axis is 21+/-12{deg} from the plane of the sky. In the A1758S system, we have measured a total mass of 4.96_-1.19_^+1.08^x10^14^M_{sun}_ and, using radial velocity data, we found that the main merger axis is located at 70+/-4{deg} from the plane of the sky, therefore closest to the line of sight.
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- ID:
- ivo://CDS.VizieR/J/A+A/629/A83
- Title:
- Complexity of magnetic fields on red dwarfs
- Short Name:
- J/A+A/629/A83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Generation, amplification, and evolution of magnetic fields in cool stars can be investigated by measuring the Zeeman effect in atomic and molecular lines observed in their spectra. In particular, Zeeman line broadening and polarization have been used for detecting magnetic fields in stellar atmospheres. Similar to the Sun, these fields are complex and height-dependent (i.e., comprise 3D structures) and require advanced diagnostics. Fortunately, many molecular lines dominating M-dwarf spectra, such as FeH, CaH, MgH, and TiO, are temperature- and Zeeman- sensitive and form at different atmospheric heights, which makes them excellent probes of magnetic fields on M dwarfs. Our goal is to analyze the complexity of magnetic fields in M dwarfs. We investigate how magnetic fields vary with the stellar temperature (i.e., mass) and how "surface" inhomogeneities are distributed in height - the dimension that is usually neglected in stellar magnetic studies. This is achieved by including many atomic and molecular species in our study. We have determined effective temperatures of the photosphere and of magnetic features, magnetic field strengths and filling factors for nine M dwarfs (M1-M7). Our chi^2^ analysis is based on a comparison of observed and synthetic intensity and circular polarization profiles (Stokes I and V) of many magnetically sensitive atomic and molecular lines in ten wavelength regions. Stokes profiles were calculated by solving polarized radiative transfer equations under the local thermodynamic equilibrium using model atmospheres. We have found that properties of magnetic structures depend on the analyzed atomic or molecular species and their formation heights within the atmosphere. Two types of magnetic features similar to those on the Sun have been found: one is cooler (starspots), while the other one is hotter (network, small-scale magnetic features). The magnetic field strength in both starspots and network is within 3kG to 6kG, on average it is 5kG for the M1-M7 spectral class range. These fields occupy a large fraction of M dwarf atmospheres at all heights, up to 100%. The plasma beta is less than one throughout the entire M dwarf atmospheres, implying that they are highly magnetized stars. A combination of many molecular and atomic species and a simultaneous analysis of intensity and circular polarization spectra have allowed us to better decipher the complexity of magnetic fields on M dwarfs, including their dependence on the height within the atmosphere. This work provides an opportunity to investigate a larger sample of M dwarfs as well as L-type brown dwarfs.
- ID:
- ivo://CDS.VizieR/J/ApJ/845/36
- Title:
- Complex network for solar active regions
- Short Name:
- J/ApJ/845/36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we developed a complex network of solar active regions (ARs) to study various local and global properties of the network. The values of the Hurst exponent (0.8-0.9) were evaluated by both the detrended fluctuation analysis and the rescaled range analysis applied on the time series of the AR numbers. The findings suggest that ARs can be considered as a system of self-organized criticality (SOC). We constructed a growing network based on locations, occurrence times, and the lifetimes of 4227 ARs recorded from 1999 January 1 to 2017 April 14. The behavior of the clustering coefficient shows that the AR network is not a random network. The logarithmic behavior of the length scale has the characteristics of a so-called small-world network. It is found that the probability distribution of the node degrees for undirected networks follows the power law with exponents of about 3.7-4.2. This indicates the scale-free nature of the AR network. The scale-free and small-world properties of the AR network confirm that the system of ARs forms a system of SOC. Our results show that the occurrence probability of flares (classified by GOES class C>5, M, and X flares) in the position of the AR network hubs takes values greater than that obtained for other nodes.
- ID:
- ivo://CDS.VizieR/J/A+A/641/A54
- Title:
- Complex organic molecules in high-mass SFRs
- Short Name:
- J/A+A/641/A54
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have studied four complex organic molecules (COMs), the oxygen-bearing methyl formate (CH_3_OCHO) and dimethyl ether (CH_3_OCH_3_) as well as the nitrogen-bearing formamide (NH_2_CHO) and ethyl cyanide (C_2_H_5_CN), towards a large sample of 39 high-mass star-forming regions representing different evolutionary stages, from early to evolved phases. We aim to identify potential correlations and chemical links between the molecules and to trace their evolutionary sequence through the star formation process. We analysed spectra obtained at 3, 2, and 0.9mm with the IRAM-30m telescope. We derived the main physical parameters for each species by fitting the molecular lines. We compared them and evaluated their evolution while also taking several other interstellar environments into account. We report detections in 20 sources, revealing a clear dust absorption effect on column densities. Derived abundances range between ~10^-10^-10^-7^ for CH_3_OCHO and CH_3_OCH_3_, ~10^-12^-10^-10^ for NH_2_CHO, and ~10^-11^-10^-9^ for C_2_H_5_CN. The abundances of CH3OCHO, CH3OCH3, and C2H5CN are very strongly correlated (r>=0.92) across 4 orders of magnitude.We note that CH_3_OCHO and CH_3_OCH_3_ show the strongest correlations in most parameters, and a nearly constant ratio (1) over a remarkable 9 orders of magnitude in luminosity for the following wide variety of sources: pre-stellar to evolved cores, low- to high-mass objects, shocks, Galactic clouds, and comets. This indicates that COMs chemistry is likely early developed and then preserved through evolved phases. Moreover, the molecular abundances clearly increase with evolution, covering 6 orders of magnitude in the luminosity/mass ratio. We consider CH_3_OCHO and CH_3_OCH_3_ to be most likely chemically linked. They could, for example, share a common precursor, or be formed one from the other. Based on correlations, ratios, and the evolutionary trend, we propose a general scenario for all COMs, involving a formation in the cold, earliest phases of star formation and a following increasing desorption with the progressive thermal and shock-induced heating of the evolving core.
- ID:
- ivo://CDS.VizieR/J/A+A/639/A87
- Title:
- Complex organic mol. in low-mass protostars
- Short Name:
- J/A+A/639/A87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Complex organic molecules (COMs) are thought to form on icy dust grains in the earliest phase of star formation. The evolution of these COMs from the youngest Class 0/I protostellar phases toward the more evolved Class II phase is still not fully understood. Since planet formation seems to start early, and mature disks are too cold for characteristic COM emission lines, studying the inventory of COMs on Solar- System scales in the Class 0/I stage is relevant. Our aim is to determine the abundance ratios of oxygen-bearing COMs in Class 0 protostellar systems on scales of ~100AU radius. We aim to compare these abundances with one another, and to the abundances of other low-mass protostars such as IRAS16293-2422B and HH 212. Additionally, using both cold and hot COM lines, the gas-phase abundances can be tracked from a cold to a hot component, and ultimately be compared with those in ices to be measured with the James Webb Space Telescope (JWST). The abundance of deuterated methanol allows us to probe the ambient temperature during the formation of this species. ALMA Band 3 (3mm) and Band 6 (1mm) observations are obtained for seven Class 0 protostars in the Perseus and Serpens star-forming regions. By modeling the inner protostellar region using local thermodynamic equilibrium (LTE) models, the excitation temperature and column densities are determined for several O-bearing COMs including methanol (CH_3_OH), acetaldehyde (CH_3_CHO), methyl formate (CH_3_OCHO), and dimethyl ether (CH_3_OCH_3_). Abundance ratios are taken with respect to CH_3_OH. Three out of the seven of the observed sources, B1-c, B1-bS (both Perseus), and Serpens S68N (Serpens), show COM emission. No clear correlation seems to exist between the occurrence of COMs and source luminosity. The abundances of several COMs such as CH_3_OCHO, CH_3_OCH_3_, acetone (CH_3_COCH_3_), and ethylene glycol ((CH_2_OH)2) are remarkably similar for the three COM-rich sources; this similarity also extends to IRAS 16238-2422B and HH 212, even though collectively these sources originate from four different star-forming regions (i.e., Perseus, Serpens, Ophiuchus, and Orion). For other COMs like CH_3_CHO, ethanol (CH_3_CH_2_OH), and glycolaldehyde (CH_2_OHCHO), the abundances differ by up to an order of magnitude, indicating that local source conditions become important. B1-c hosts a cold (Tex=60K), more extended component of COM emission with a column density of typically a few percent of the warm/hot (Tex=200K) central component. A D/H ratio of 1-3% is derived for B1-c, S68N, and B1-bS based on the CH_2_DOH/CH_3_OH ratio (taking into account statistical weighting) suggesting a temperature of ~15K during the formation of methanol. This ratio is consistent with other low-mass protostars, but is lower than for high-mass star-forming regions. The abundance ratios of most O-bearing COMs are roughly fixed between different star-forming regions, and are presumably set at an earlier cold prestellar phase. For several COMs, local source properties become important. Future mid-infrared facilities such as JWST/MIRI will be essential for the direct observation of COM ices. Combining this with a larger sample of COM-rich sources with ALMA will allow ice and gas-phase abundances to be directly linked in order to constrain the routes that produce and maintain chemical complexity during the star formation process.
- ID:
- ivo://CDS.VizieR/J/A+A/629/A112
- Title:
- Complex refractive index of CO ice
- Short Name:
- J/A+A/629/A112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Reliable, directly measured optical properties of astrophysical ice analogs in the infrared (IR) and terahertz (THz) range are missing. These parameters are of great importance to model the dust continuum radiative transfer in dense and cold regions, where thick ice mantles are present, and are necessary for the interpretation of future observations planned in the far-IR region. Coherent THz radiation allows direct measurement of the complex dielectric function (refractive index) of astrophysically relevant ice species in the THz range. The time-domain waveforms and the frequency-domain spectra of reference samples of CO ice, deposited at a temperature of 28.5K and annealed to 33K at different thicknesses, have been recorded. A new algorithm is developed to reconstruct the real and imaginary parts of the refractive index from the time-domain THz data. The complex refractive index in the wavelength range of 1mm-150um (0.3-2.0THz) has been determined for the studied ice samples, and compared with available data found in the literature. The developed algorithm of reconstructing the real and imaginary parts of the refractive index from the time-domain THz data enables, for the first time, the determination of optical properties of astrophysical ice analogs without using the Kramers-Kronig relations. The obtained data provide a benchmark to interpret the observational data from current ground based facilities as well as future space telescope missions, and have been used to estimate the opacities of the dust grains in presence of CO ice mantles.
- ID:
- ivo://CDS.VizieR/J/ApJ/897/83
- Title:
- Component structure in the neightborhood of IC 443
- Short Name:
- J/ApJ/897/83
- Date:
- 11 Mar 2022
- Publisher:
- CDS
- Description:
- We present the results of a detailed investigation into the physical conditions in interstellar material interacting with the supernova remnant (SNR) IC443. Our analysis is based on a comprehensive examination of high-resolution far-ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope of two stars behind IC443. One of our targets (HD43582) probes gas along the entire line of sight through the SNR, while the other (HD254755) samples material located ahead of the primary supernova shock front. We identify low-velocity quiescent gas in both directions and find that the densities and temperatures in these components are typical of diffuse atomic and molecular clouds. Numerous high- velocity components are observed in the absorption profiles of neutral and singly ionized atomic species toward HD43582. These components exhibit a combination of greatly enhanced thermal pressures and significantly reduced dust-grain depletions. We interpret this material as cooling gas in a recombination zone far downstream from shocks driven into neutral gas clumps. The pressures derived for a group of ionized gas components at high positive velocity toward HD43582 are lower than those of the other shocked components, pointing to pressure inhomogeneities across the remnant. A strong, very high velocity component near -620km/s is seen in the absorption profiles of highly ionized species toward HD43582. The velocity of this material is consistent with the range of shock velocities implied by observations of soft thermal X-ray emission from IC443. Moderately high velocity gas toward HD254755 may represent shocked material from a separate foreground SNR.
- ID:
- ivo://CDS.VizieR/VIII/39
- Title:
- Composite CO Survey of the Milky Way
- Short Name:
- VIII/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This survey consists of CO(J=1-0) (115 GHz) spectra for the entire Galactic plane. The latitude coverage varies with longitude and in some regions extends from -25 degrees to +25 degrees. The observations were made with the Columbia/GISS 1.2m telescope in New York City, and a twin telescope on Cerro Tololo in Chile. The angular resolution of the survey is 30' (square), the velocity resolution is 1.3km/s and the sensitivity ranges from about 0.1K/chan to 0.35K/chan. The survey is presented as 720 latitude-velocity maps in FITS format, one for each 30' of longitude from -180.0 deg to +179.5 deg, and one velocity-integrated map covering the entire plane. The velocity range of each file is -300 km/s to +300 km/s. The survey has been updated to include some additional data, more careful reprojections of the regions that were originally mapped in equatorial coordinates, and improved estimates of the absolute calibration of the CO intensities (Digel and Dame 1995, unpublished).
- ID:
- ivo://CDS.VizieR/J/ApJ/475/469
- Title:
- Composite HST Spectrum of Quasars
- Short Name:
- J/ApJ/475/469
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We construct a composite quasar spectrum from 284 HST FOS spectra of 101 quasars with redshifts z>0.33. The spectrum covers the wavelengths between 350 and 3000A in the rest frame, with a peak S/N level of ~130 per A at ~1200A. Since ~90% of the sample quasars have redshift z<1.5, the spectrum is suitable for studying the wavelength region shortward of Ly{alpha} without large effects from intervening Ly{alpha} forest absorption. Data in the waveband between 350 and 600A are mainly from the spectra of z>1.5 quasars, for which significant corrections for the accumulated Lyman-series line and continuum absorption have been applied. There is a significant steepening of the continuum slope around 1050A. The continuum between 1050 and 2200A can be modeled as a power law f_{nu} proportional to {nu}_{alpha}_ with {alpha}=-0.99+/-0.05. For the full sample the power-law index in the extreme ultraviolet (EUV) between 350 and 1050A is {alpha}=-1.96+/-0.15. For the radio-loud subsample (60 objects), the EUV spectral index is {alpha}~=-2.2, while for the radio-quiet subsample (41 objects) it is {alpha}~=-1.8. The continuum flux in the wavelengths near the Lyman limit shows a depression of ~10%. The break in the power-law index and the slight depression of the continuum near the Lyman limit are features expected in Comptonized accretion-disk spectra. Comptonization produces a power-law tail in the wavelength band shortward of 1000A and smears out the Lyman-limit edge of the intrinsic accretion-disk spectrum. In the EUV waveband, we detect several possible emission features, including one around 690A that may be O III + N III produced by the Bowen fluorescence effect. Comparing our composite spectrum with one made at higher redshifts by Francis et al. (1991ApJ...373..465F), we find that the equivalent widths of Ly{alpha} and high-ionization emission lines are larger in our sample, reflecting a known luminosity dependence. The equivalent widths of low-ionization lines do not exhibit such a dependence, suggesting that the quasar EUV continuum above ~50eV is steeper at higher luminosity. Radio-quiet quasars appear to show a slightly harder continuum and lower ionization levels in their emission lines.
- ID:
- ivo://CDS.VizieR/J/ApJ/849/53
- Title:
- Composite SEDs of type 1 and type 2 QSOs
- Short Name:
- J/ApJ/849/53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present observed mid-infrared and optical colors and composite spectral energy distributions (SEDs) of type 1 (broad-line) and 2 (narrow-line) quasars selected from Sloan Digital Sky Survey (SDSS) spectroscopy. A significant fraction of powerful quasars are obscured by dust and are difficult to detect in optical photometric or spectroscopic surveys. However, these may be more easily identified on the basis of mid-infrared (MIR) colors and SEDs. Using samples of SDSS type 1 and 2 matched in redshift and [OIII] luminosity, we produce composite rest-frame 0.2-15{mu}m SEDs based on SDSS, UKIDSS, and Wide-field Infrared Survey Explorer photometry and perform model fits using simple galaxy and quasar SED templates. The SEDs of type 1 and 2 quasars are remarkably similar, with the differences explained primarily by the extinction of the quasar component in the type 2 systems. For both types of quasar, the flux of the active galactic nucleus (AGN) relative to the host galaxy increases with AGN luminosity (L_[OIII]_) and redder observed MIR color, but we find only weak dependencies of the composite SEDs on mechanical jet power as determined through radio luminosity. We conclude that luminous quasars can be effectively selected using simple MIR color criteria similar to those identified previously (W1-W2>0.7; Vega), although these criteria miss many heavily obscured objects. Obscured quasars can be further identified based on optical-IR colors (for example, (u-W3[AB]>1.4(W1-W2[Vega])+3.2). These results illustrate the power of large statistical studies of obscured quasars selected on the basis of MIR and optical photometry.