Thursday, April 27, 2006

diskpbb and nsatmos added to v12

Added diskpbb and nsatmos to v12 for the new release. Note that nsatmos requires an ascii data file which was added to Xspec/src/spectral/modelIonData.

Keywords: HEAsoft, xspec

Wednesday, April 26, 2006

Natarajan: Weak Lensing

UMCP astronomy colloquium by Priya Natarajan from Yale. She summarized the effects of gravitational lensing and described her work deriving the poperties of subhaloes in clusters. She fits a smooth cluster distribution then a subhalo at the position of every cluster galaxy. 10-15% of the mass of the cluster is in the subhaloes which are individually more extended than the visible light of the galaxy. She essentially does a two-parameter fit for the subhalo properties assuming that all subhaloes in the cluster have similar properties. Recent extension of this work which is in press finds evidence for tidal truncation with smaller haloes in the center of the cluster. Finally she talked about prospects for investigating dark energy by comparing the lensing of background objects of different known redshifts. In this case the details of the lens drop out and the distance ratios to the background objects can be determined and hence the cosmology.

Keywords: clusters, lensing

Using Hera in xselect

Modified the xsl_xmm_epic_makeresp perl script so that when saving spectra in xselect and requesting a response matrix then Hera is used if SAS is not available on the local machine. I will make a similar modification to xsl_chandra_acis_makeresp when the appropriate updates are made to Hera to support it.

Keywords: xselect, HEAsoft, Hera, XMM

Tuesday, April 25, 2006

Lawrence Principe: Alchemy

Science colloquium by Larry Principe from JHU - professor in both chemistry and history of science departments. His principal argument is that alchemy is the legitimate forerunner to chemistry and alchemists have received an unfairly bad press. Many alchemists were extremely careful, observant, and dedicated experimenters. He showed pages from one alchemists lab notebook which looked similar to modern lab notebooks in the way that hypotheses were developed and tested by careful experiments. The idea of changing base metals to gold was based on a theory that all metals were composed of different amounts of philosophical mercury and philosophical sulphur. Study of alchemy is made difficult by the practice of alchemists encoding their public utterances. Fortunately, there are some private letters and notes that provide clues to the codes used. Part of Principe's research has been to decipher formulae for turning base metals into gold and then reproduce the experiments to find out what the alchemists were actually doing. He provided a recent example where the experiment produced a striking dendritic fractal structure looking very like a tree. Principe surmises that this explains the presence of trees in allegorical alchemical illustrations.

Monday, April 24, 2006


Suebsuwong et al. discuss the effects of light bending on the reflection spectrum from disks around black holes.

Jaffe et al. explore methods for fitting templates to CMB data.

Bock et al. is the final report of a DoE/NSF/NASA task force on the future of CMB measurements providing a roadmap for precision polarization measurements.

Stanek et al. observe that star formation occurs in galaxies with low O abundances and that long GRBs appear to correlate with star formation implying that the Milky Way is unlikely to have hosted a long GRB in the last few billion years.

LaRoque et al combine Chandra X-ray and OVRO/BIMA SZ measurements of 38 massive clusters. They find consistency with an isothermal model outside the cluster core and determine the gas mass fraction within r2500. Assuming this is constant with redshift the results are consistent with the standard LCDM cosmology.

Rodriguez et al. report the detection using VLBA of a SMBH binary with a separation of only 7.3 pc.

Loeb proposes searching for evidence of planets in nearby dwarf galaxies. Since these galaxies were formed at z~10 this would argue that planets can form when the Universe was 10^3 times as dense which would contradict the anthropic argument that a low cosmological constant is required for planet formation.

Brown et al. use HST to measure the size of UB313 and find it 5% larger than Pluto. The V band albedo is 86%.

Mahajan et al. point out that if the cosmological constant is surmised to be due the zero-point energy with a suitable ultraviolet cut-off scale to get the correct value then this is testable using observations of the Casimir effect. The constraint from observation requires a zero-point value 10^12 times larger than required for the cosmological constant.

Wilson et al. discuss their plan to use Spitzer surveys to find clusters in the 1 < z < 2 'desert'.

Thursday, April 20, 2006

PIE and PANDA regions in extractor

Modifications to extractor region code. For PIE region fixed incorrect definition of the angle so now consistent with ds9 and other regions and fixed error that threw out all events with angle > 180 degrees. Added support for PANDA region but only for the case of one sector and one annulus. For regions in WCS coordinates correct for any CROTA in use for the input event file.
(extractor v4.64.)

Keywords : extractor, xselect, HEAsoft

Wednesday, April 19, 2006

Mark Krumholz: Turbulence, Feedback, and Slow Star Formation

UMCP astronomy colloquium by Mark Krumholz, a postdoc at Princeton after doing his PhD at Berkeley. The major mystery of star formation is why it is so slow - the SFR is 100 times smaller than predicted based on free fall times. Krumholz & McKee have developed a theory where turbulence holds up star formation and the turbulence itself is produced by star formation. He showed that a fairly simple physical theory reproduces the observation results. The remaining problems are taking into account magnetic fields and explaining the 100 km/s turbulence seen in starbursts.

Keywords : star formation

xronos window output from extractor

Fixed a bug that caused incorrect time ranges in the xronos window output (created for instance by extr curve in xselect). This was reported by Gulab Dewangan at CMU. There is still an unresolved issue if the selected region overlaps multiple chips with separate GTIs. The xronos output file contains the GTI for the final chip (in numerical order). This fix is extractor v4.63.

Keywords: xselect, extractor, HEAsoft

Tuesday, April 18, 2006

Don Lamb: Short GRBs

EUD seminar by Don Lamb. He summarized the story from last year on short GRBs then talked extensively about a HETE burst that appears short but has a photometric redshift of 1.5 (if heavily reddened) or 4.6. He suggested that there are problems with a classification scheme based on spectral hardness since results appear not to be consistent between different missions. The T90 classification also has issues because it is measured in the observed frame. If long GRBs are cosmological then the rest frame durations are much shorter (by 1+z) so the distinction between short and long is eroded. Finally he noted that the presence of a spectral lag is a good classifier of a long GRB but there are some short bursts with negligible lag but large error bars implying they are not highly structured (so lag cannot be well-measured) so these might actually be similar to long bursts.

Keywords: GRB

Monday, April 17, 2006


Hudson et al. analyze Chandra observations of the double jet radio source 3C 75 at the core of Abell 400 and conclude that the two AGN are a bound system from a previous merger.

Rigby et al. consider why half of X-ray selected AGN are optically dull and conclude that extranuclear dust in the host galaxy plays an important role.

Stewart describes a procedure for matched filter detection of point sources in XMM images.

Ettori & Fabian argue that He sedimentation timescales in clusters were lower in the past leading to supersolar He abundances in the cores. This has the effect of reducing the measured metal abundances in these regions.

Wilson et al. use Chandra observations to investigate the bright limbs of the cavities in Cygnus A finding a weak shock and suggesting that the jet power is going into heating the ICM.

Barkhouse et al. present a survey for X-ray detected clusters in 130 archival Chandra pointings that are part of CHAMP.

Sandage et al. summarize their 15 year program to calibrate the SN Ia Hubble diagram using HST observations of Cepheids in nearby galaxies. They derive H0 = 62.3 +/- 1.5 (stat) +/- 5.0 (syst).

Kaaret et al find a 62 +/- 2.5 day period in the X-rays from the ULX source in M82.

Egami et al. describe Spitzer observations of BCGs and note an overall trend that clusters with shorter cooling times harbor more IR luminous BCGs.

Wednesday, April 12, 2006


Kravtsov et al. use mock Chandra images of cluster simulations to compare X-ray estimators for the total mass and show that the new estimator Yx is remarkably good.

Werner et al. look at very hot AGB stars which are thought to have consumed their H shells exposing nucleosynthesis products.

Ascasibar & Markevitch use simulations of cluster mergers to show that cold fronts are caused by the sloshing of the cool gas in the central gravitational potential well.

Wednesday, April 05, 2006

warning messages from znibin and inibin

Both inibin and znibin (in the NEI code cont.f) generate a warning if the response energies extend beyond the available model data. Ensured that these warning messages are written out once not every iteration. This will be in next v11 and v12 releases.

Keywords: xspec, heasoft