896 research outputs found
Detection of a new methanol maser line with ALMA
Aims. We aimed at investigating the structure and kinematics of the gaseous
disk and outflows around the massive YSO S255 NIRS3 in the S255IR-SMA1 dense
clump. Methods. Observations of the S255IR region were carried out with ALMA at
two epochs in the compact and extended configurations. Results. We
serendipitously detected a new, never predicted, bright maser line at about
349.1 GHz, which most probably represents the CHOH A transition. The emission covers most of the 6.7 GHz methanol maser emission
area of almost 1 in size and shows a velocity gradient in the
same sense as the disk rotation. No variability was found on the time interval
of several months. It is classified as Class II maser and probably originates
in a ring at a distance of several hundreds AU from the central star.Comment: 4 pages, 4 figures, accepted by Astronomy and Astrophysic
Oxygen abundance distributions in six late-type galaxies based on SALT spectra of HII regions
Spectra of 34 H II regions in the late-type galaxies NGC1087, NGC2967,
NGC3023, NGC4030, NGC4123, and NGC4517A were observed with the South African
Large Telescope (SALT). In all 34 H II regions, oxygen abundances were
determined through the "counterpart" method (C method). Additionally, in two H
II regions in which the auroral lines were detected oxygen abundances were
measured through the classic Te method. We also estimated the abundances in our
H II regions using the O3N2 and N2 calibrations and compared those with the
C-based abundances. With these data we examined the radial abundance
distributions in the disks of our target galaxies. We derived
surface-brightness profiles and other characteristics of the disks (the surface
brightness at the disk center and the disk scale length) in three photometric
bands for each galaxy using publicly available photometric imaging data. The
radial distributions of the oxygen abundances predicted by the relation between
abundance and disk surface brightness in the W1 band obtained for spiral
galaxies in our previous study are close to the radial distributions of the
oxygen abundances determined from the analysis of the emission line spectra for
four galaxies where this relation is applicable. Hence, when the
surface-brightness profile of a late-type galaxy is known, this parametric
relation can be used to estimate the likely present-day oxygen abundance in its
disk.Comment: 15 pages, 11 figures; Accepted for publication in Astronomy &
Astrophysic
Molecular line and continuum study of the W40 cloud
The dense cloud associated with W40, one of the nearby H II regions, has been
studied in millimeter-wave molecular lines and in 1.2 mm continuum. Besides,
1280 MHz and 610 MHz interferometric observations have been done. The cloud has
complex morphological and kinematical structure, including a clumpy dust ring
and an extended dense core. The ring is probably formed by the "collect and
collapse" process due to the expansion of neighboring H II region. Nine dust
clumps in the ring have been deconvolved. Their sizes, masses and peak hydrogen
column densities are: pc, and cm, respectively. Molecular lines are observed
at two different velocities and have different spatial distributions implying
strong chemical differentiation over the region. The CS abundance is enhanced
towards the eastern dust clump 2, while the NH, NH, and
HCO abundances are enhanced towards the western clumps. HCN and
HCO do not correlate with the dust probably tracing the surrounding gas.
Number densities derived towards selected positions are: cm. Two western clumps have kinetic temperatures 21 K and 16 K and
are close to virial equilibrium. The eastern clumps 2 and 3 are more massive,
have higher extent of turbulence and are probably more evolved than the western
ones. They show asymmetric CS(2--1) line profiles due to infalling motions
which is confirmed by model calculations. An interaction between ionized and
neutral material is taking place in the vicinity of the eastern branch of the
ring and probably trigger star formation.Comment: 16 pages, 6 figure
Relations between abundance characteristics and rotation velocity for star-forming MaNGA galaxies
We derive rotation curves, surface brightness profiles, and oxygen abundance
distributions for 147 late-type galaxies using the publicly available
spectroscopy obtained by the MaNGA survey. Changes of the central oxygen
abundance (O/H)_0, the abundance at the optical radius (O/H)_R25, and the
abundance gradient with rotation velocity V_rot are examined for galaxies with
rotation velocities from 90 km/s to 350 km/s. We found that each relation shows
a break at V_rot^* ~200 km/s. The central (O/H)_0 abundance increases with
rising V_rot and the slope of the (O/H)_0 - V_rot relation is steeper for
galaxies with V_rot < V_rot^*. The mean scatter of the central abundances
around this relation is 0.053 dex. The relation between the abundance at the
optical radius of a galaxy and its rotation velocity is similar; the mean
scatter in abundances around this relation is 0.081 dex. The radial abundance
gradient expressed in dex/kpc flattens with the increase of the rotation
velocity. The slope of the relation is very low for galaxies with V_rot >
V_rot^*. The abundance gradient expressed in dex/R25 is rougly constant for
galaxies with V_rot < V_rot^*, flattens towards V_rot^*, and then again is
roughly constant for galaxies with V_rot > V_rot^*. The change of the gradient
expressed in terms of dex/h_d (where h_d is the disc scale length) with
rotation velocity is similar to that for gradient in dex/R25. The relations
between abundance characteristics and other basic parameters (stellar mass,
luminosity, and radius) are also considered.Comment: Accepted for publication in the Astronomy and Astrophysic
Breaks in surface brightness profiles and radial abundance gradients in the discs of spiral galaxies
We examine the relation between breaks in the surface brightness profiles and
radial abundance gradients within the optical radius in the discs of 134 spiral
galaxies from the CALIFA survey. The distribution of the radial abundance (in
logarithmic scale) in each galaxy was fitted by simple and broken linear
relations. The surface brightness profile was fitted assuming pure and broken
exponents for the disc. We find that the maximum absolute difference between
the abundances in a disc given by broken and pure linear relations is less than
0.05 dex in the majority of our galaxies and exceeds the scatter in abundances
for 26 out of 134 galaxies considered. The scatter in abundances around the
broken linear relation is close (within a few percent) to that around the pure
linear relation. The breaks in the surface brightness profiles are more
prominent. The scatter around the broken exponent in a number of galaxies is
lower by a factor of two or more than that around the pure exponent. The shapes
of the abundance gradients and surface brightness profiles within the optical
radius in a galaxy may be different. A pure exponential surface brightness
profile may be accompanied by a broken abundance gradient and vise versa. There
is no correlation between the break radii of the abundance gradients and
surface brightness profiles. Thus, a break in the surface brightness profile
does not need to be accompanied by a break in the abundance gradient.Comment: 18 pages, 17 figures, accepted for publication in A&
The Spatial-Kinematic Structure of the Region of Massive Star Formation S255N on Various Scales
The results of a detailed analysis of SMA, VLA, and IRAM observations of the
region of massive star formation S255N in CO(2---1), \nh, \nhh, \co and some
other lines is presented. Combining interferometer and single-dish data has
enabled a more detailed investigation of the gas kinematics in the moleclar
core on various spatial scales. There are no signs of rotation or isotropic
compression on the scale of the region as whole. The largest fragments of gas
(0.3 pc) are located near the boundary of the regions of ionized
hydrogen S255 and S257. Some smaller-scale fragments are associated with
protostellar clumps. The kinetic temperatures of these fragments lie in the
range 10---80 K. A circumstellar torus with inner radius R
8000 AU and outer radius R 12 000 AU has been detected around the clump
SMA1. The rotation profile indicates the existence of a central object with
mass 8.5/ sin 2 (i) M . SMA1 is resolved into two clumps,
SMA1---NE and SMA1---SE, whose temperatures are 150 K and 25
K, respectively. To all appearances, the torus is involved in the accretion of
surrounding gas onto the two protostellar clumps
A Multi-Wavelength High Resolution Study of the S255 Star Forming Region. General structure and kinematics
We present observational data for two main components (S255IR and S255N) of
the S255 high mass star forming region in continuum and molecular lines
obtained at 1.3 mm and 1.1 mm with the SMA, at 1.3 cm with the VLA and at 23
and 50 cm with the GMRT. The angular resolution was from ~ 2" to ~ 5" for all
instruments. With the SMA we detected a total of about 50 spectral lines of 20
different molecules (including isotopologues). About half of the lines and half
of the species (in particular N2H+, SiO, C34S, DCN, DNC, DCO+, HC3N, H2CO,
H2CS, SO2) have not been previously reported in S255IR and partly in S255N at
high angular resolution. Our data reveal several new clumps in the S255IR and
S255N areas by their millimeter wave continuum emission. Masses of these clumps
are estimated at a few solar masses. The line widths greatly exceed expected
thermal widths. These clumps have practically no association with NIR or radio
continuum sources, implying a very early stage of evolution. At the same time,
our SiO data indicate the presence of high-velocity outflows related to some of
these clumps. In some cases, strong molecular emission at velocities of the
quiescent gas has no detectable counterpart in the continuum. We discuss the
main features of the distribution of NH3, N2H+, and deuterated molecules. We
estimate properties of decimeter wave radio continuum sources and their
relationship with the molecular material.Comment: 21 pages, 26 figures, accepted for publication in Astrophysical
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