86 research outputs found
The NN2 Flux Difference Method for Constructing Variable Object Light Curves
We present a new method for optimally extracting point-source time
variability information from a series of images. Differential photometry is
generally best accomplished by subtracting two images separated in time, since
this removes all constant objects in the field. By removing background sources
such as the host galaxies of supernovae, such subtractions make possible the
measurement of the proper flux of point-source objects superimposed on extended
sources. In traditional difference photometry, a single image is designated as
the ``template'' image and subtracted from all other observations. This
procedure does not take all the available information into account and for
sub-optimal template images may produce poor results. Given N total
observations of an object, we show how to obtain an estimate of the vector of
fluxes from the individual images using the antisymmetric matrix of flux
differences formed from the N(N-1)/2 distinct possible subtractions and provide
a prescription for estimating the associated uncertainties. We then demonstrate
how this method improves results over the standard procedure of designating one
image as a ``template'' and differencing against only that image.Comment: Accepted to AJ. To be published in November 2005 issue. 16 page, 2
figures, 2 tables. Source code available at
http://www.ctio.noao.edu/essence/nn2
Beryllium in the Ultra-Lithium-Deficient,Metal-Poor Halo Dwarf, G186-26
The vast majority of low-metal halo dwarfs show a similar amount of Li; this
has been attributed to the Li that was produced in the Big Bang. However, there
are nine known halo stars with T 5900 K and [Fe/H] 1.0 that are
ultra-Li-deficient. We have looked for Be in the very low metallicity star, G
186-26 at [Fe/H] = 2.71, which is one of the ultra-Li-deficient stars. This
star is also ultra-Be deficient. Relative to Be in the Li-normal stars at
[Fe/H] = 2.7, G 182-26 is down in Be by more than 0.8 dex. Of two potential
causes for the Li-deficiency -- mass-transfer in a pre-blue straggler or extra
rotationally-induced mixing in a star that was initially a very rapid rotator
-- the absence of Be favors the blue-straggler hypothesis, but the rotation
model cannot be ruled-out completely.Comment: Accepted for Ap.J. Letters 10 pages, 4 figure
An X-ray review of MS1054-0321: hot or not?
XMM-Newton observations are presented for the z=0.83 cluster of galaxies
MS1054-0321, the highest redshift cluster in the Einstein Extended Medium
Sensitivity Survey (EMSS). The temperature inferred by the XMM-Newton data,
T=7.2 (+0.7, -0.6) keV, is much lower than the temperature previously reported
from ASCA data, T=12.3 (+3.1, -2.2) keV (Donahue et al. 1998), and a little
lower than the Chandra temperature, T=10.4(+1.7, -1.5) keV, determined by
Jeltema et al. 2001. The discrepancy between the newly derived temperature and
the previously derived temperatures is discussed in detail. If one allows the
column density to be a free parameter, then the best fit temperature becomes
T=8.6 (+1.2, -1.1) keV, and the best fit column density becomes N_(H)=1.33
(+0.15 -0.14) x 10^20 atoms/cm^2. The iron line is well detected in the
XMM-Newton spectrum with a value for the abundance of Z=0.33 (+0.19 -0.18)
Zsol, in very good agreement with previous determinations. The derived XMM
X-ray luminosity for the overall cluster in the 2-10 keV energy band is
L_X=(3.81 +/- 0.19) x 10^44 h^-2 erg s^-1 while the bolometric luminosity is
L_BOL=(8.05+/-0.40) x 10^44 h^-2 erg s^-1. The XMM-Newton data confirm the
substructure in the cluster X-ray morphology already seen by ROSAT and in much
more detail by Chandra. The central weak lensing clump is coincident with the
main cluster component and has a temperature T=8.1 (+1.3, -1.2) keV. The
western weak lensing clump coincides with the western X-ray component which is
much cooler with a temperature T=5.6 (+0.8, -0.6)$ keV. Given the newly
determined temperature, MS1054-0321 is no longer amongst the hottest clusters
known.Comment: To appear in the A&A main Journal, 13 pages including 3 postscript
figures and 4 tables. Figs. 1, 4, 5 and 7 are too large and are not given
here. The whole paper as pdf file is posted at
http://www.ira.cnr.it/~gioia/PUB/publications.htm
Beryllium and Alpha-Element Abundances in a Large Sample of Metal-Poor Stars
The light elements, Li, Be, and B, provide tracers for many aspects of
astronomy including stellar structure, Galactic evolution, and cosmology. We
have taken spectra of Be in 117 metal-poor stars ranging in metallicity from
[Fe/H] = -0.5 to -3.5 with Keck I + HIRES at a resolution of 42,000 and
signal-to-noise ratios of near 100. We have determined the stellar parameters
spectroscopically from lines of Fe I, Fe II, Ti I and Ti II. The abundances of
Be and O were derived by spectrum synthesis techniques, while abundances of Fe,
Ti, and Mg were found from many spectral line measurements. There is a linear
relationship between [Fe/H] and A(Be) with a slope of +0.88 +-0.03 over three
orders of magnitude in [Fe/H]. We fit the relationship between A(Be) and [O/H]
with both a single slope and with two slopes. The relationship between [Fe/H]
and [O/H] seems robustly linear and we conclude that the slope change in Be vs.
O is due to the Be abundance. Although Be is a by-product of CNO, we have used
Ti and Mg abundances as alpha-element surrogates for O in part because O
abundances are rather sensitive to both stellar temperature and surface
gravity. We find that A(Be) tracks [Ti/H] very well with a slope of 1.00
+-0.04. It also tracks [Mg/H] very well with a slope of 0.88 +-0.03. We find
that there are distinct differences in the relationships of A(Be) and [Fe/H]
and of A(Be) and [O/H] for our dissipative stars and our accretive stars. We
suggest that the Be in the dissipative stars was primarily formed by GCR
spallation and Be in the accretive stars was formed in the vicinity of SN II.Comment: Accepted for Ap.J. Nov. 10, 2011, v. 741 70 pages, 27 figures, 5
table
project: III. Gas mass fraction shape in high redshift clusters
We study the gas mass fraction, behavior in
project. The typical shape of high redshift galaxy
clusters follows the global shape inferred at low redshift quite well. This
result is consistent with the gravitational instability picture leading to self
similar structures for both the dark and baryonic matter. However, the mean
XMM$ clusters, the apparent gas
fraction at the virial radius is consistent with a non-evolving universal value
in a high matter density model and not with a concordance.Comment: Accepted, A&A, in pres
23 High Redshift Supernovae from the IfA Deep Survey: Doubling the SN Sample at z>0.7
We present photometric and spectroscopic observations of 23 high redshift
supernovae spanning a range of z=0.34-1.03, 9 of which are unambiguously
classified as Type Ia. These supernovae were discovered during the IfA Deep
Survey, which began in September 2001 and observed a total of 2.5 square
degrees to a depth of approximately m=25-26 in RIZ over 9-17 visits, typically
every 1-3 weeks for nearly 5 months, with additional observations continuing
until April 2002. We give a brief description of the survey motivations,
observational strategy, and reduction process. This sample of 23 high-redshift
supernovae includes 15 at z>0.7, doubling the published number of objects at
these redshifts, and indicates that the evidence for acceleration of the
universe is not due to a systematic effect proportional to redshift. In
combination with the recent compilation of Tonry et al. (2003), we calculate
cosmological parameter density contours which are consistent with the flat
universe indicated by the CMB (Spergel et al. 2003). Adopting the constraint
that Omega_total = 1.0, we obtain best-fit values of (Omega_m,
Omega_Lambda)=(0.33, 0.67) using 22 SNe from this survey augmented by the
literature compilation. We show that using the empty-beam model for
gravitational lensing does not eliminate the need for Omega_Lambda > 0.
Experience from this survey indicates great potential for similar large-scale
surveys while also revealing the limitations of performing surveys for z>1 SNe
from the ground.Comment: 67 pages, 12 figures, 12 tables, accepted for publication in the
Astrophysical Journa
The XMMâNEWTON ⊠Project: I. The X-ray luminosity â temperature relation at z>0.4
We describe XMM-Newton Guaranteed Time observations of a sample of eight high redshift (0.45 < z < rvirial) bolometric luminosities, performed ÎČ-model fits to the radial surface profiles and made spectral fits to a single temperature isothermal model. We describe data analysis techniques that pay particular attention to background mitigation. We have also estimated temperatures and luminosities for two known clusters (Abell 2246 and RXJ1325.0-3814), and one new high redshift cluste r candidate (XMMU J084701.8 +345117), that were detected o ff-axis. Characterizing the L x â Tx relation as L x = L 6 ( T 6keV ) α , we find L 6 = 15 . 9 + 7 . 6 â 5 . 2 Ă 1044erg s â 1 and α =2.7 ±0.4 for an ⊠Π= 0 . 0 , ⊠M = 1 .0, H0 = 50 km s â 1 Mpc â 1 cosmology at a typical redshift z ⌠0 .55. Comparing with the low redshift study by Markevitch, 1998, we find α to be in agreement, and assuming L x â Tx to evolve as (1 + z ) A , we find A =0.68 ±0.26 for the same cosmology and A = 1 .52 + 0 .26 â 0 .27 for an ⊠Π= 0 . 7 , ⊠M = 0 . 3 cosmology. Our A values are very similar to those found previously by Vikhlinin et al., 2002 using a compilation of Chandra observations of 0 .39 < z < 1 .26 clusters. We conclude that there is now evidence from both XMM-Newton and Chandra for an evolutionary trend in the L x â Tx relation. This evolution is significantly below the level expected from the predictions of the self-similar model for an ⊠Π= 0 . 0 , ⊠M = 1 .0, cosmology, but consistent with self-similar model in an ⊠Π= 0 . 7 , ⊠M = 0 . 3 cosmology. Our observations lend support to the robustness and completeness of the SHARC and 160SD surveys
The XMM-LSS survey: the Class 1 cluster sample over the initial 5 square degrees and its cosmological modelling
We present a sample of 29 galaxy clusters from the XMM-LSS survey over an
area of some 5deg2 out to a redshift of z=1.05. The sample clusters, which
represent about half of the X-ray clusters identified in the region, follow
well defined X-ray selection criteria and are all spectroscopically confirmed.
For all clusters, we provide X-ray luminosities and temperatures as well as
masses. The cluster distribution peaks around z=0.3 and T =1.5 keV, half of the
objects being groups with a temperature below 2 keV. Our L-T(z) relation points
toward self-similar evolution, but does not exclude other physically plausible
models. Assuming that cluster scaling laws follow self-similar evolution, our
number density estimates up to z=1 are compatible with the predictions of the
concordance cosmology and with the findings of previous ROSAT surveys. Our well
monitored selection function allowed us to demonstrate that the inclusion of
selection effects is essential for the correct determination of the evolution
of the L-T relation, which may explain the contradictory results from previous
studies. Extensive simulations show that extending the survey area to 10deg2
has the potential to exclude the non-evolution hypothesis, but that constraints
on more refined ICM models will probably be limited by the large intrinsic
dispersion of the L-T relation. We further demonstrate that increasing the
dispersion in the scaling laws increases the number of detectable clusters,
hence generating further degeneracy [in addition to sigma8, Omega_m, L(M,z) and
T(M,z)] in the cosmological interpretation of the cluster number counts. We
provide useful empirical formulae for the cluster mass-flux and mass-count-rate
relations as well as a comparison between the XMM-LSS mass sensitivity and that
of forthcoming SZ surveys.Comment: Accepted for publication by MNRAS. Full resolution images as well as
additional cluster data are available through a dedicated database at
http://l3sdb.in2p3.fr:8080/l3sdb
The XMM--NEWTON Omega Project: II.Cosmological implications from the high redshift L-T relation of X-ray clusters
The evolution with redshift of the temperature-luminosity relation of X-ray
galaxy clusters is a key ingredient to break degeneracies in the interpretation
of X-ray clusters redshift number counts. We therefore take advantage of the
recent measurements of the temperature-luminosity relation of distant clusters
observed with XMM-Newton and Chandra satellites to examine theoretical number
counts expected for different available X-rays cluster samples, namely the
RDCS, EMSS, SHARC, 160deg^2 and the MACS at redshift greater than 0.3. We
derive these counts without any adjustment, using models previously normalized
to the local temperature distribution function and to the high-z (z = 0.33)
TDF. We find that these models having Omega_M in the range [0.85-1.] predict
counts in remarkable agreement with the observed counts in the different
samples. We illustrate that this conclusion is weakly sensitive to the various
ingredients of the modeling. Therefore number counts provide a robust evidence
of an evolving population. A realistic flat low density model (Omega_M = 0.3),
normalized to the local abundance of clusters is found to overproduce cluster
abundance at high redshift (above z = 0.5) by nearly an order of magnitude.
This result is in conflict with the popular concordance model. The conflict
could indicate a deviation from the expected scaling of the M-T relation with
redshift.Comment: 5 pages, 7 figures, A&A Letters, accepte
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