92 research outputs found
Interstellar CN and CH+ in Diffuse Molecular Clouds: 12C/13C Ratios and CN Excitation
We present very high signal-to-noise ratio absorption-line observations of CN
and CH+ along 13 lines of sight through diffuse molecular clouds. The data are
examined to extract precise isotopologic ratios of 12CN/13CN and 12CH+/13CH+ in
order to assess predictions of diffuse cloud chemistry. Our results on
12CH+/13CH+ confirm that this ratio does not deviate from the ambient 12C/13C
ratio in local interstellar clouds, as expected if the formation of CH+
involves nonthermal processes. We find that 12CN/13CN, however, can be
significantly fractionated away from the ambient value. The dispersion in our
sample of 12CN/13CN ratios is similar to that found in recent surveys of
12CO/13CO. For sight lines where both ratios have been determined, the
12CN/13CN ratios are generally fractionated in the opposite sense compared to
12CO/13CO. Chemical fractionation in CO results from competition between
selective photodissociation and isotopic charge exchange. An inverse
relationship between 12CN/13CN and 12CO/13CO follows from the coexistence of CN
and CO in diffuse cloud cores. However, an isotopic charge exchange reaction
with CN may mitigate the enhancements in 12CN/13CN for lines of sight with low
12CO/13CO ratios. For two sight lines with high values of 12CO/13CO, our
results indicate that about 50 percent of the carbon is locked up in CO, which
is consistent with the notion that these sight lines probe molecular cloud
envelopes where the transition from C+ to CO is expected to occur. An analysis
of CN rotational excitation yields a weighted mean value for T_01(12CN) of
2.754 +/- 0.002 K, which implies an excess over the temperature of the cosmic
microwave background of only 29 +/- 3 mK. This modest excess eliminates the
need for a local excitation mechanism beyond electron and neutral collisions.
The rotational excitation temperatures in 13CN show no excess over the
temperature of the CMB.Comment: 27 pages, 21 figures, emulateapj style, accepted for publication in
Ap
Galactic Evolution of Nitrogen
We present detailed spectroscopic analysis of nitrogen abundances in 31
unevolved metal-poor stars analysed by spectral synthesis of the near-UV NH
band at 3360 A observed at high resolution with various telescopes. We found
that [N/Fe] scales with that of iron in the metallicity range -3.1 < [Fe/H] <0
with the slope 0.01+-0.02. Furthermore, we derive uniform and accurate (N/O)
ratios using oxygen abundances from near-UV OH lines obtained in our previous
studies. We find that a primary component of nitrogen is required to explain
the observations. The NH lines are discovered in the VLT/UVES spectra of the
very metal-poor subdwarfs G64-12 and LP815-43 indicating that these stars are N
rich. The results are compared with theoretical models and observations of
extragalactic HII regions and Damped Ly systems. This is the first
direct comparison of the (N/O) ratios in these objects with those in Galactic
stars.Comment: 10 pages, 6 figures, to appear in Astronomy and Astrophysic
Molecular hydrogen at z=1.973 toward Q0013-004: Dust depletion pattern in damped Lyman-alpha systems
We study the dust depletion pattern in eight well separated components of the
z=1.973, logN(HI)=20.83, damped Lyman-alpha system toward Q0013-004, four of
which have detectable H2 absorption. The apparent correlation between the
abundance ratios [Fe/S] and [Si/S] in the components indicates that the
abundance pattern is indeed due to dust-depletion. In particular, we find
evidence for depletion similar to what is observed in cold gas of the Galactic
disk ([Fe/Zn]=-1.59, Fe/S=-1.74, Zn/S=-0.15, [Si/S]=-0.85) in one of the
weakest components in which molecular hydrogen is detected with logN(H2)=16.5.
This is the first time such a large depletion is seen in a DLA system. This
observation supports the possibility that current samples of DLA systems might
be biased against the presence of cold and dusty gas along the line of sight.
The overall metallicities of this peculiar DLA system in which OI and CII are
spread over 1050 km/s are [P/H]=-0.64, [Zn/H]=-0.74 and [S/H]=-0.82 relative to
solar. The sub-DLA system at z=1.96753 has [P/H]>0.06, [Zn/H]>-0.02 and
[S/H]>-0.18. The overall molecular fraction is in the range -2.7<logf<-0.6. CO
is not detected (logN(CO)/N(HI)<-8) and HD could be present at z=1.97380. We
show that the presence of H2 is closely related to the physical conditions of
the gas: high particle density together with low temperature. The observed
excitation of high J H2 levels and the molecular fraction show large variations
from one component to the other suggesting that the UV radiation field is
highly inhomogeneous throughout the system. Gas pressure, estimated from CI
absorptions, is larger than what is observed in the ISM of our Galaxy. All this
is probably a consequence of intense star-formation activity in the vicinity of
the absorbing gas. (Abridged)Comment: 9 pages, 8 figures, MNRAS Latex. Accepted for publication in MNRA
A new 21-cm absorber identified with an galaxy
We present Giant Metrewave Radio Telescope (GMRT) observations of redshifted
21-cm absorption from the metal line absorption system towards PKS
1243-072. HI absorption is clearly detected; the absorption profile has a
velocity spread of km/s. Detection of 21-cm absorption indicates that
the absorber has an HI column density large enough to be classified as a damped
Lyman- system. Follow up ground based optical imaging and spectroscopy
allow us to identify the absorber with an galaxy at an impact
parameter of kpc from the line of sight to the QSO. The absorbing
galaxy is unusual in that it has bright emission lines. On the basis of the
optical spectrum we are unable to uniquely classify the galaxy since its
emission line ratios lie in the transition region between starburst and Seyfert
II type spectra.Comment: 5 pages, 3 figures. Accepted for publication in Astronomy &
Astrophysic
A near-solar metallicity damped Lyman-alpha system toward the BAL quasar Tol 1037-2703
We report the detection of a Broad Absorption Line (BAL) outflow in the
spectrum of Tol 1037-2703 with three main BALs at 36000, 25300 and 22300~\kms
outflow velocities. Although the overall flow is dominated by high ionization
lines like and C IV, the gas of highest velocity shows absorption from Mg I, Mg
II and Fe II. Covering factor arguments suggest that the absorbing complexes
are physically associated with the QSO and have transverse dimensions smaller
than that of the UV continuum emitting region (r<0.1 pc). We show that the C IV
absorption at \zabs=2.082 has a covering factor 0.86 and the absorption
profile has varied over the last four years. The detection of absorption from
excited fine structure levels of C II and Si II in narrow components embedded
in the C IV trough reveals large density inhomogeneities. IR pumping is the
most likely excitation process. The \zabs=2.139 system is a damped system with
log N(H I) ~ 19.7. The weakness of the metal lines together with the high
quality of the data make the metallicity measurements particularly reliable.
The absolute metallicity is close to solar with [Zn/H]=-0.26. The
-chain elements have metallicities consistently solar (respectively
+0.05, -0.02, -0.03 and -0.15 for [Mg/H], [Si/H], [P/H] and [S/H]) and iron
peak elements are depleted by a factor of about two ([Fe/Zn], [Cr/Zn], [Mn/Zn]
and [Ni/Zn] are equal to -0.39, -0.27, -0.49, -0.30). Lines from C I are
detected but H is absent with a molecular fraction less than
8. High metallicity and low nitrogen abundance, [N/Zn]=-1.40,
favor the idea that metals have been released by massive stars during a
starburst of less than 0.5 Gyr of age. (abridged)Comment: To appear in A & A, 12 pages, latex, 15 figure
Pharmacological evaluation of Prosopis ruscifolia extract on lipid profile in hyperglycemic and hyperlipidemic mice
La diabetes es una patología crónica grave, con efectos a largo plazo que incluyen daño a los vasos sanguíneos o dislipidemia diabética. La dislipidemia diabética se caracteriza por el aumento de las concentraciones de triglicéridos de baja densidad y lipoproteínas y una disminución de las lipoproteínas de alta densidad HDL-colesterol (HDL-c). Este estudio tuvo como objetivo evaluar el efecto de Prosopis ruscifolia sobre el perfil lipídico en ratones suizos albinos con hiperglucemia e hiperlipidemia.CONACYT – Consejo Nacional de Ciencia y TecnologíaPROCIENCI
Photoionized OVI absorbers toward the bright QSO HE 0515-4414
We report on detailed Monte Carlo inversion analysis of five OVI systems from
the spectrum of the bright quasar HE 0515-4414 (z_e = 1.71). The associated
system at z_a = 1.697 with the neutral hydrogen column density N(HI)= 4.4
10^{13} cm^{-2} shows pronounced absorption from highly ionized transitions of
CIII, CIV, NV, OVI, SiIV, and probably SVI. We found that only a power law type
ionizing spectrum (J_nu propto nu^{-1.5}) is consistent with the observed
sample of the line profiles, i.e. the system is definitely intrinsic. The
relative metal abundances give almost the solar pattern and the metallicity of
about 5 times solar. The system originates in a thin shell of the line-of-sight
thickness L <= 16 pc. Two OVI systems at z_a = 1.674 ([C/H] = -1.6) and 1.602
([O/H] = -1.1), arising in intervening halos, have linear sizes of L = 3-14 kpc
and 17 kpc, respectively. Absorption systems at z_a = 1.385 ([C/H] = -0.3, L =
1.7-2.5 kpc) and z_a = 1.667 ([C/H] = -0.5, L = 1 kpc) exhibit characteristics
very similar to that observed in metal-enriched high velocity clouds in the
Milky Way.These systems are probably embedded in extremely metal-poor halos
with [C/H] < -2.4 (z_a = 1.667) and [C/H] < -3.7 (z_a = 1.385). We also found
two additional extremely metal-poor Ly-alpha systems at z_a = 1.500 and 1.681
with, respectively, N(HI) = 1.7 10^{15} and 1.8 10^{15} cm^{-2} and [C/H] <
-4.0 and <-3.0, - an indication that the distribution of metals in the
metagalactic medium is utterly patchy. Our results show that the ionization
states in the analyzed OVI absorbers, ranging from z = 1.4 to 1.7, can be
maintained by photoionization only and that the fraction of the shock-heated
hot gas with temperature T > 10^5 K is negligible in these systems.Comment: 16 pages, including 11 PostScript figures. Accepted for publication
in A&
Uneventful Disappearance of a Large Left Atrial Ball Thrombus with Enoxaparin in a Patient with Mitral Stenosis Associated with Pregnancy
An atrial thrombus is a relatively common echocardiographic finding in patients with mitral valve stenosis (MVS) and atrial fibrillation (AF). However, a “ball thrombus” or floating thrombus in the left atrium is a rare and specific entity associated with MVS. A 24-year-old woman with rheumatic MVS presented with complaints of progressive dyspnea and inferior limbs edema that began 23 days earlier after a caesarean operation for stillbirth carried out at 8 months of pregnancy. At the time of hospitalization, she was in New York Heart Association functional class III and the ECG showed sinus rhythm. Transthoracic color-flow Doppler echocardiography revealed a thick, stenotic mitral valve with a valvular area of 0.9 cm2, and an echogenic large left-atrial mass diagnosed as a free-floating left-atrial thrombus that was corroborated by transesophageal echocardiography. She refused surgery and was treated medically, and low molecular weight heparin (LMWH) (enoxaparin 80 mg/12 h) was given for 14 days and was discharged uneventfully on coumarin. Two days before discharge, a transthoracic and transesophageal ecocardiography showed disappearance of the ball thrombus uneventfully leaving spontaneous echo contrast inside the left atrium. To the best of our knowledge, this is the first case showing disappearance of a giant left atrial ball thrombus with LMWH treatment in a patient with severe MVS during sinus rhythm associated with pregnancy
Spatial variation in the fine-structure constant -- new results from VLT/UVES
(abridged) We present a new analysis of a large sample of quasar
absorption-line spectra obtained using UVES (the Ultraviolet and Visual Echelle
Spectrograph) on the VLT (Very Large Telescope) in Chile. In the VLT sample
(154 absorbers), we find evidence that alpha increases with increasing
cosmological distance from Earth. However, as previously shown, the Keck sample
(141 absorbers) provided evidence for a smaller alpha in the distant absorption
clouds. Upon combining the samples an apparent variation of alpha across the
sky emerges which is well represented by an angular dipole model pointing in
the direction RA=(17.3 +/- 1.0) hr, dec. = (-61 +/- 10) deg, with amplitude
(0.97 +0.22/-0.20) x 10^(-5). The dipole model is required at the 4.1 sigma
statistical significance level over a simple monopole model where alpha is the
same across the sky (but possibly different to the current laboratory value).
The data sets reveal a number of remarkable consistencies: various data cuts
are consistent and there is consistency in the overlap region of the Keck and
VLT samples. Assuming a dipole-only (i.e. no-monopole) model whose amplitude
grows proportionally with `lookback-time distance' (r=ct, where t is the
lookback time), the amplitude is (1.1 +/- 0.2) x 10^(-6) GLyr^(-1) and the
model is significant at the 4.2 sigma confidence level over the null model
[Delta alpha]/alpha = 0). We apply robustness checks and demonstrate that the
dipole effect does not originate from a small subset of the absorbers or
spectra. We present an analysis of systematic effects, and are unable to
identify any single systematic effect which can emulate the observed variation
in alpha.Comment: 47 pages, 35 figures. Accepted for publication by Monthly Notices of
the Royal Astronomical Society. Please see
http://astronomy.swin.edu.au/~mmurphy/pub.html for an ASCII version of table
A1 and the full set of Voigt profile fits for appendix
First Stars XIV. Sulfur abundances in extremely metal-poor (EMP) stars
Sulfur is important: the site of its formation is uncertain, and at very low
metallicity the trend of [S/Fe] against [Fe/H] is controversial. Below
[Fe/H]=-2.0, [S/Fe] remains constant or it decreases with [Fe/H], depending on
the author and the multiplet used in the analysis. Moreover, although sulfur is
not significantly bound in dust grains in the ISM, it seems to behave
differently in DLAs and in old metal-poor stars. We aim to determine precise S
abundance in a sample of extremely metal-poor stars taking into account NLTE
and 3D effects. NLTE profiles of the lines of the multiplet 1 of SI have been
computed using a new model atom for S. We find sulfur in EMP stars to behave
like the other alpha-elements, with [S/Fe] remaining approximately constant for
[Fe/H]<-3. However, [S/Mg] seems to decrease slightly as a function of [Mg/H].
The overall abundance patterns of O, Na, Mg, Al, S, and K are best matched by
the SN model yields by Heger & Woosley. The [S/Zn] ratio in EMP stars is solar,
as found also in DLAs. We obtain an upper limit on the abundance of sulfur,
[S/Fe] < +0.5, for the ultra metal-poor star CS 22949-037. This, along with a
previous reported measurement of zinc, argues against the conjecture that the
light-element abundances pattern in this star, and, by analogy, the hyper
metal-poor stars HE 0107-5240 and HE 1327-2326, are due to dust depletion.Comment: 10 pages, accepted for publication in A&
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