735 research outputs found
Germanium and lead: Significant differences between meteoritic and photospheric abundances?
The order of the Galactic cosmic ray source (GCRS) composition in terms of first ionization potential (FIP) was examined. For most elements, the degree of volatility is (positively) correlated with the value of the FIP, so that it is not easy to distinguish a correlation of GCRS abundances anomalies with FIP from a correlation with volatility. Only a few permit to distinguish between the two kinds of ordering: if they are depleted relative to refractory metals, volatility must be relevant, if not, FIP is relevant. Among them Cu and Zn would seem to favor FIP. Among the best indicators are Ge and Pb. The abundance anomalies in GCRS are defined relative to a standard which, for the heavy elements concerned, is commonly taken as C1 Carbonaceous Chondrites. Photospheric abundances are more directly representative of the protosolar nebula, and hence of ordinary local galactic (LG) matter. The Ge and Pb reference abundance determinations in the Photosphere and in C1 meteorites are examined and their relevance to the problem with FIP vs. volatility in GCRs is discussed
New solar opacities, abundances, helioseismology, and neutrino fluxes
We construct solar models with the newly calculated radiative opacities from
the Opacity Project (OP) and recently determined (lower) heavy element
abundances. We compare results from the new models with predictions of a series
of models that use OPAL radiative opacities, older determinations of the
surface heavy element abundances, and refinements of nuclear reaction rates.
For all the variations we consider, solar models that are constructed with the
newer and lower heavy element abundances advocated by Asplund et al. (2005)
disagree by much more than the estimated measuring errors with
helioseismological determinations of the depth of the solar convective zone,
the surface helium composition, the internal sound speeds, and the density
profile. Using the new OP radiative opacities, the ratio of the 8B neutrino
flux calculated with the older and larger heavy element abundances (or with the
newer and lower heavy element abundances) to the total neutrino flux measured
by the Sudbury Neutrino Observatory is 1.09 (0.87) with a 9% experimental
uncertainty and a 16% theoretical uncertainty, 1 sigma errors.Comment: ApJ Letters (in press), added 3 references, detailed numerical solar
models and distributions of neutrino fluxes available at
http://www.sns.ias.edu/~jnb (models go back to 1982
The Dark Matter Radial Profile in the Core of the Relaxed Cluster A2589
We present an analysis of a Chandra--ACIS observation of the galaxy cluster
A2589 to constrain the radial distribution of the total gravitating matter and
the dark matter in the core of the cluster. A2589 is especially well-suited for
this analysis because the hot gas in its core region (r < ~0.1 Rvir) is
undisturbed by interactions with a central radio source. From the largest
radius probed (r=0.07 Rvir) down to r ~0.02 Rvir dark matter dominates the
gravitating mass. Over this region the radial profiles of the gravitating and
dark matter are fitted well by the NFW and Hernquist profiles predicted by CDM.
The density profiles are also described well by power laws, rho ~r^{-alpha},
where alpha=1.37 +/- 0.14 for the gravitating matter and alpha=1.35 +/- 0.21
for the dark matter. These values are consistent with profiles of CDM halos but
are significantly larger than alpha ~0.5 found in LSB galaxies and expected
from self-interacting dark matter models.Comment: 10 pages, 6 figures, To Appear in The Astrophysical Journal, March 20
issue, a few very minor changes to match copyedited versio
Line formation in solar granulation VI. [C I], C I, CH and C2 lines and the photospheric C abundance
The solar photospheric carbon abundance has been determined from [C I], C I,
CH vibration-rotation, CH A-X electronic and C2 Swan electronic lines by means
of a time-dependent, 3D, hydrodynamical model of the solar atmosphere.
Departures from LTE have been considered for the C I lines. These turned out to
be of increasing importance for stronger lines and are crucial to remove a
trend in LTE abundances with the strengths of the lines. Very gratifying
agreement is found among all the atomic and molecular abundance diagnostics in
spite of their widely different line formation sensitivities. The mean of the
solar carbon abundance based on the four primary abundance indicators ([C I], C
I, CH vibration-rotation, C_2 Swan) is log C = 8.39 +/- 0.05, including our
best estimate of possible systematic errors. Consistent results also come from
the CH electronic lines, which we have relegated to a supporting role due to
their sensitivity to the line broadening. The new 3D based solar C abundance is
significantly lower than previously estimated in studies using 1D model
atmospheres.Comment: Accepted for A&A, 13 page
Ni abundance in the core of the Perseus Cluster: an answer to the significance of resonant scattering
Using an XMM-Newton observation of the Perseus cluster we show that the
excess in the flux of the 7-8 keV line complex previously detected by ASCA and
BeppoSAX is due to an overabundance of Nickel rather than to an anomalously
high Fe He/Fe He ratio. This observational fact leads to the
main result that resonant scattering, which was assumed to be responsible for
the supposed anomalous Fe He/Fe He ratio, is no longer required.
The absence of resonant scattering points towards the presence of significant
gas motions (either turbulent or laminar) in the core of the Perseus cluster.Comment: 29 pages, 10 bw figures, accepted for publication in the
Astrophysical Journa
Metallicity structure in X-ray bright galaxy groups
Using Chandra X-ray data of a sample of 15 X-ray bright galaxy groups, we
present preliminary results of a coherent study of the radial distribution of
metal abundances in the hot gas in groups. The iron content in group outskirts
is found to be lower than in clusters by a factor of ~2, despite showing mean
levels in the central regions comparable to those of clusters. The abundance
profiles are used to constrain the contribution from supernovae type Ia and II
to the chemical enrichment and thermal energy of the intragroup medium at
different group radii. The results suggest a scenario in which a substantial
fraction of the chemical enrichment of groups took place in filaments prior to
group collapse.Comment: 5 pages, 2 figures. To appear in the proceedings of ESO Astrophysics
Symposia: "Groups of Galaxies in the Nearby Universe", eds. I. Saviane, V.
Ivanov, J. Burissova (Springer
On The Progenitor of the Type II-Plateau Supernova 2003gd in Messier 74
HST WFPC2 archival F606W and F300W images obtained within one year prior to
the explosion of the nearby Type II supernova (SN) 2003gd in Messier 74 (NGC
628) have been analyzed to isolate the progenitor star. The SN site was located
using precise astrometry applied to the HST images. Two plausible candidates
are identified within 0.6" of the SN position in the F606W image. Neither
candidate was detected in the F300W image. SN 2003gd appears to be of Type
II-plateau (II-P), with age ~87 d on June 17 UT and with low reddening [E(B-V)
= 0.13 mag]. The most likely of the two progenitor candidates has M_V_0 ~ -3.5
mag (for an extinction-corrected distance modulus of 29.3 mag) and, based on
additional color information derived from a high-quality, archival ground-based
I-band image, we estimate that this star was a red supergiant with initial mass
M_ZAMS ~ 8 -- 9 Msun. This mass estimate is somewhat lower than, but relatively
consistent with, recent limits placed on the progenitor masses of other SNe
II-P, using HST data. Future HST imaging with the Advanced Camera for Surveys,
when the SN has faded considerably, will be extremely useful in pinpointing the
exact SN location and securing identification of the progenitor. If our
proposed candidate is confirmed, it will be only the sixth SN progenitor ever
directly identified.Comment: 10 pages, 6 figures, to appear now in PASP, 2003 Nov. This update
includes more detailed light and color curves for the S
Discovery of excess O I absorption towards the z = 6.42 QSO SDSS J1148+5251
We present a search for O I in the spectra of nine 4.9 < z_qso < 6.4 QSOs
taken with Keck/HIRES. We detect six systems with N(O I) > 10^13.7 cm^{-2} in
the redshift intervals where O I 1302 falls redward of the Ly-alpha forest.
Four of these lie towards SDSS J1148+5251 (z_qso = 6.42). This imbalance is
unlikely to arise from variations in sensitivity among our data or from a
statistical fluctuation. The excess O I occurs over a redshift interval that
also contains transmission in Ly-alpha and Ly-beta. Therefore, if these O I
systems represent pockets of neutral gas, then they must occur within or near
regions of the IGM that are highly ionized. In contrast, no O I is detected
towards SDSS J1030+0524 (z_qso = 6.30), whose spectrum shows complete
absorption in Ly-alpha and Ly-beta over \Delta z ~ 0.2. Assuming no ionization
corrections, we measure mean abundance ratios = -0.04 +/- 0.06,
= -0.31 +/- 0.09, and = -0.34 +/- 0.07 (2 sigma), which are
consistent with enrichment dominated by Type II supernovae. The O/Si ratio
limits the fraction of silicon in these systems contributed by metal-free very
massive stars to < 30%, a result which is insensitive to ionization
corrections. The ionic comoving mass densities along the z_qso > 6.2
sightlines, including only the detected systems, are \Omega(O I) = (7.0 +/-
0.6) * 10^{-8}, \Omega(Si II) = (9.6 +/- 0.9) * 10^{-9}, and \Omega(C II) =
(1.5 +/- 0.2) * 10^{-8}.Comment: Submitted to ApJ, with changes to reflect referee's comment
The Mid-infrared Fine-structure Lines of Neon as an Indicator of Star For mation Rate in Galaxies
The fine-structure lines of singly ([Ne II] 12.8 micron) and doubly ([Ne III]
15.6 micron) ionized neon are among the most prominent features in the
mid-infrared spectra of star-forming regions, and have the potential to be a
powerful new indicator of the star formation rate in galaxies. Using a sample
of star-forming galaxies with measurements of the fine-structure lines
available from the literature, we show that the sum of the [Ne II] and [Ne III]
luminosities obeys a tight, linear correlation with the total infrared
luminosity, over 5 orders of magnitude in luminosity. We discuss the formation
of the lines and their relation with the Lyman continuum luminosity. A simple
calibration between star formation rate and the [Ne II]+[Ne III] luminosity is
presented.Comment: To appear in ApJ. 8 page
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