203 research outputs found
Detection of the linear radical HC4N in IRC+10216
We report the detection of the linear radical HC4N in the C-rich envelope of
IRC+10216. After HCCN, HC4N is the second member of the allenic chain family
HC_(2n)N observed in space. The column density of HC4N is found to be 1.5
10**12 cm**(-2). The abundance ratio HC2N/HC4N is 9, a factor of two larger
than the decrement observed for the cyanopolyynes HC$_(2n+1)N/HC_(2n+3)N.
Linear HC_4N has a 3-Sigma electronic ground state and is one of the 3
low-energy isomeric forms of this molecule. We have searched for the bent and
ringed HC4N isomers, but could only derive an upper limit to their column
densities of about 3 10**(12) cm**(-2).Comment: Preprint of 10 page
Isotopic ratios at z=0.68 from molecular absorption lines toward B 0218+357
Isotopic ratios of heavy elements are a key signature of the nucleosynthesis
processes in stellar interiors. The contribution of successive generations of
stars to the metal enrichment of the Universe is imprinted on the evolution of
isotopic ratios over time. We investigate the isotopic ratios of carbon,
nitrogen, oxygen, and sulfur through millimeter molecular absorption lines
arising in the z=0.68 absorber toward the blazar B 0218+357. We find that these
ratios differ from those observed in the Galactic interstellar medium, but are
remarkably close to those in the only other source at intermediate redshift for
which isotopic ratios have been measured to date, the z=0.89 absorber in front
of PKS1830-211. The isotopic ratios in these two absorbers should reflect
enrichment mostly from massive stars, and they are indeed close to the values
observed toward local starburst galaxies. Our measurements set constraints on
nucleosynthesis and chemical evolution models.Comment: Accepted for publication in Astronomy & Astrophysics; 10 pages, 9
figure
Detection of CO in the inner part of M31's bulge
We report the first detection of CO in M31's bulge. The 12CO (1-0) and (2-1)
lines are both detected in the dust complex D395A/393/384, at 1.3" (~0.35 kpc)
from the centre. From these data and from visual extinction data, we derive a
CO-luminosity to reddening ratio (and a CO-luminosity to H_2 column density
ratio) quite similar to that observed in the local Galactic clouds. The (2-1)
to (1-0) line intensity ratio points to a CO rotational temperature and a gas
kinetic temperature > 10 K. The molecular mass of the complex, inside a 25'
(100 pc) region, is 1.5 10^4 Mo.Comment: 5 pages including 4 figures (2 in colour
A new infrared band in the Interstellar and Circumstellar Clouds: C_4 or C_4H?
We report on the detection with the Infrared Space Observatory (ISO) of a
molecular band at 57.5 microns (174 cm^{-1}) in carbon-rich evolved stars and
in Sgr B2. Taking into account the chemistry of these objects the most
likelihood carrier is a carbon chain. We tentatively assign the band to the
nu_5 bending mode of C_4 for which a wavenumber of 170-172.4 cm^{-1} has been
derived in matrix experiments (Withey et al. 1991). An alternate carrier might
be C_4H, although the frequency of its lowest energy vibrational bending mode,
nu_7, is poorly known (130-226 cm^{-1}). If the carrier is C_4, the derived
maximum abundance is nearly similar to that found for C_3 in the interstellar
and circumstellar media by Cernicharo, Goicoechea & Caux (2000). Hence,
tetra-atomic carbon could be one of the most abundant carbon chain molecules in
these media.Comment: 11 pages, 1 figure, accepted in ApJ Letter
Detection of circumstellar CH2CHCN, CH2CN, CH3CCH and H2CS
We report on the detection of vinyl cyanide (CH2CHCN), cyanomethyl radical
(CH2CN), methylacetylene (CH3CCH) and thioformaldehyde (H2CS) in the C-rich
star IRC +10216. These species, which are all known to exist in dark clouds,
are detected for the first time in the circumstellar envelope around an AGB
star. The four molecules have been detected trough pure rotational transitions
in the course of a 3 mm line survey carried out with the IRAM 30-m telescope.
The molecular column densities are derived by constructing rotational
temperature diagrams. A detailed chemical model of the circumstellar envelope
is used to analyze the formation of these molecular species. We have found
column densities in the range 5 x 10^(12)- 2 x 10^(13) cm^(-2), which
translates to abundances relative to H2 of several 10^(-9). The chemical model
is reasonably successful in explaining the derived abundances through gas phase
synthesis in the cold outer envelope. We also find that some of these
molecules, CH2CHCN and CH2CN, are most probably excited trough infrared pumping
to excited vibrational states. The detection of these species stresses the
similarity between the molecular content of cold dark clouds and C-rich
circumstellar envelopes. However, some differences in the chemistry are
indicated by the fact that in IRC +10216 partially saturated carbon chains are
present at a lower level than those which are highly unsaturated, while in
TMC-1 both types of species have comparable abundances.Comment: 9 pages, 5 figures; accepted for publication in A&
13CO at the centre of M82
Using the IRAM interferometer, we have observed the nearby starburst galaxy
M82 with a 4.2" resolution (~70 pc) in the 1->0 line of 13CO and in the 2.6-mm
continuum.
The spatial distribution of the 13CO line shows the same gross features as
the 12CO(1->0) map of Shen & Lo (1995), namely two lobes and a compact central
source, though with different relative intensities. The lobes are more
conspicuous and the central source is fainter in 13CO than in 12CO.
The velocity field observed around the nucleus shows a very steep gradient
(140 km/s over 75 pc), which is very probably caused by the stellar bar visible
in the near infrared. The dynamical centre coincides with the IR peak and is
shifted 6" north-east of the compact 13CO source. The two CO lobes appear to be
associated with the ends of the bar and not with a molecular ring, as usually
assumed. They are probably shaped by the strong UV radiation from the central
region. 13CO must be more photodissociated than the self-shielded 12CO
molecules in the central ~250 pc region, which may explain the relative
weakness of the 13CO central source.
A 130 pc-wide bubble of molecular gas has been identified, which happens to
host the most luminous compact radio source in M82. It lies 120 pc west of the
IR peak between the central source and the western lobe and seems characterized
by warmer gas, strong UV radio free-free radiation, and an enhanced cosmic ray
production rate.Comment: Accepted by A&A; 9 pages, 9 ps figures, needs LaTeX 2e A&A macro and
psfig Styl
Afg3p, a mitochondrial atp-dependent metalloprotease, is involved in degradation of mitochondrially-encoded cox1, cox3, cob, su6, su8 and su9 subunits of the inner membrane complex-III, complex-IV and complex-V
AbstractThe yeast AFG3 gene encodes an ATP-dependent metalloprotease belonging to a subgroup of the AAA-family. This protease has been suggested to be essential for a metal- and ATP-dependent breakdown of incompletely mitochondrially synthesized polypeptides in the inner membrane, a process proposed to be important for mitochondrial function (Pajic et al. (1994) FEBS Lett. 353, 201–206). Here, we confirm the proteolytic activity by site-directed mutagenesis and demonstrate that the proteins Cox1, Cox3, Cob, Su6, Su8 and Su9 are substrates of Afg3p. Surprisingly, this proteolytic activity is not required for respiratory function and thus presumably also not essential for mitochondrial biogenesis
Laboratory And Astronomical Detection Of The Negative Molecular Ion C3N-
The negative molecular ion C3N- has been detected at millimeter wavelengths in a low-pressure laboratory discharge, and then with frequencies derived from the laboratory data in the molecular envelope of IRC+10216. Spectroscopic constants derived from laboratory measurements of 12 transitions between 97 and 378 GHz allow the rotational spectrum to be calculated well into the submillimeter-wave band to 0.03 km s(-1) or better in equivalent radial velocity. Four transitions of C3N- were detected in IRC+10216 with the IRAM 30 m telescope at precisely the frequencies calculated from the laboratory measurements. The column density of C3N- is 0.5% that of C3N, or approximately 20 times greater than that of C4H- relative to C4H. The C3N- abundance in IRC+10216 is compared with a chemical model calculation by Petrie & Herbst. An upper limit in TMC-1 for C3N- relative to C3N (< 0.8%) and a limit for C4H- relative to C4H (< 0.004%) that is 5 times lower than that found in IRC+10216, were obtained from observations with the NRAO 100 m Green Bank Telescope (GBT). The fairly high concentration ofNRFKorean government MEST 2012R1A1A1014646, 2012M4A2026720Southeast Physics Network (SEP-Net)Science and Technology Facilities Council ST/F002858/1, ST/I000976/1Swedish Research Council 2009-4088U.S. NSF AST-0708176, AST-1009799NASA NNX07AH09G, NNG04G177G, NNX11AE09GChandra grant SAO TM8-9009XBiochemistr
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