In the past years, my main interest have been in large scale surveys and in particular in the detection of variable objects. For this purpose I have developed as part of my thesis a difference image pipeline with my collaborators (mainly Chris Stubbs,Gajus Miknaitis, Anthony Miceli, Andy Becker, Gene Magnier & collaborators at CTIO and LLNL). This pipeline is or will be used for various projects (see Loneos, SuperMacho, SDSS SN, w-project). I have also worked on the core properties of early-type galxies with Frank van den Bosch, Milos Milosavljevic, David Merritt, and collaborators at JHU. As my first project at UW I build a seeing monitor (see DIMM). I have also continued to work with my old group at PSU (Erik Bodegom, Ralf Widenhorn, Lars Muenderman) on properties of CCD detectors.
 

Difference Imaging Pipeline

We (mainly Chris Stubbs, Gajus Miknaitis, Anthony Miceli, Andy Becker, Gene Magnier & collaborators at CTIO and LLNL) have developed a difference image pipeline in which new images are calibrated, matched to archival template images of each field, aligned to sub-pixel accuracy, convolved to account for differences in seeing, then subtracted and added to the database. The pipeline is divided into self-contained 'black boxes'. This makes is possible to build a custom-made pipeline for each individual project out of these building blocks. Documentation will soon be available.
 

Loneos RR Lyrae: Probing the Galactic Structure

In the past, the Galaxy's potential in its outermost region has been probed mainly with the dynamics of satellite galaxies. However, this yields large uncertanties, depending upon whether the satellites are bound to our Galaxy and whether the entire system is in equlibrium, given the long orbital timescales. A novel way to probe the potential in this realm is to use tidal streams of disrupted dwarf galaxies since they trace the orbital path in the potential. Besides the Magellanic Stream, the only other full-fledged tidal stream detected has been the Sagittarius Dwarf galaxy, which currently is on a pass through the Galactic disk (Yanni et al. 2000; Ivezic et al. 2000; Vivas et al.  2001; Ibata et al. 2001). However, theoretical work predicts an abundant number of tidal streams of disrupted dwarf galaxies. An adequate tracer for such streams are RR Lyrae stars since their intrinsic magnitude is known, allowing accurate distance estimates. The detection of such streams using RR Lyrae stars is hampered by the fact that not only a wide spatial coverage and deep limiting magnitude are needed, but also a high temporal coverage.

During the past four years, the Lowell Observatory Near Earth Object Survey (LONEOS) has imaged nearly half of the sky in multiple epochs. With one of the first versions of the reductions pipelein a database was created containing 15000 sq. deg. with >8 epochs and 6000 sq. deg. with >20 epochs down to V = 19 magnitudes. This makes it ideal for studying variable objects, such as RR Lyrae stars, cataclysmic variables, and quasars (see AAS'02a poster). From this dataset, thousands of candidate RR Lyrae stars have already been extracted and will be used to identify and track tidal streams (see AAS'02b poster). In order to gather more dynamical information about the tidal stream, the line-of-sight velocity of the RR-Lyrae stars must be measured. Having the spatial coordinates, the radial velocity and the orbital path of the streams, which comprises nearly the complete 6D phase space information, an unprecedented way of tracing the Galactic potential and probing the structure, extent and shape of its dark matter halo will be opened. In the near future, we will start rereducing all available data. The resulting database will tripling the spatial and temporal coverage currently available.
 

SuperMaCHO project

A next generationmicrolensing survey of the LMC, the SuperMACHO project, probes the nature and distribution of the Galactic dark matter by searching for the transient brightening of background stars due to gravitational lensing by foreground MACHOs (MAssive Compact Halo Objects). Its predecessor, the MACHO project, has detected about two dozen of these events, setting important limits on the amount of dark matter in astronomical objects (Alcock et al.). However, an order of magnitude more events is needed to properly estimate the density of the lens population. Also, in order to distinguish between the different populations acting as the lenses and characterize their properties, one can exploit exotic microlensing events, which occur in roughly 10% of the events seen to date. The features of these exotic events can lift the standard microlensing degeneracy between mass, location and velocity of the lens. The SuperMACHO project will likely increase the number of events by a factor of ten and will lift it out of the realm of small number statistics. For more information you can check out the Supermacho Homepage.

In the first run last year we tested and implemented our difference image pipeline. Current efforts are concentrated on the downstream end, in particalur extraction, vizualisation and classification tools for the database.

SDSS SN search

During the last three months of each calendar year, the Sloan Digital Sky Survey (SDSS) carries out repeated images of sections of sky in the Southern Galactic Cap, as the Northern Galactic hemisphere, which is the primary survey objective, is unobservable at these times. These images will be stacked to create deeper slice to complement the Northern survey, but they also provide a unique opportunity for a variability study. Imaging is carried out in drift-scan mode (on the 2.5m SDSS telescope at Apache Point, NM), resulting in data "stripes", which for the Southern survey lie along the celestial equator and span roughly 90 degrees in right ascension,  totaling ~225 square degrees of sky.  With an observing cadence of 3 to 5 days, this survey provides an excellent chance to detect new supernova (SN) events. Gajus Miknaitis utilizes our difference image pipeline to detect low-z SN (see AAS'02c poster) as part of his PhD thesis.

w-project

One way of characterizing the dark energy that appears to produce the accelerating universe is by an equation of state P = w r, where w is between -1/3 and -1. The w-project's goal is to measure the value of w by using supernovae of type Ia as standard candles. Since the w-project will share nights with the Supermacho project at CTIO starting fall'2002 and since both projects have very similar reduction steps, we will use the same difference image pipeline for both projects. This is an effort of the High-Z SN Search Team in conjunction with the Supermacho Team.
 

Core Properties of Early-Type Galaxies

We (Frank van den Bosch & collaborators at JHU and Leiden) investigate the core properties of early-type galaxies with 67 HST images (see core-properties page for paper and figures). The sample show a wide variety of morphology, in particular dust (see dust-paper), embedded stellar disks and bars. To a large extent we confirm the clear dichotomy found in previous HST surveys: bright, boxy ellipticals with shallow inner cusps (`core' galaxies) on one hand and faint, disky ellipticals with steep central cusps (`power-law' galaxies) on the other hand. The advantages and shortcomings of classification schemes utilizing the extrapolated central cusp slope are discussed, and it is shown that this cusp slope  might be an inadequate representation for galaxies whose luminosity profile slope changes smoothly with radius rather than resembling a broken power-law. In fact, we find evidence for an `intermediate' class of galaxies, that cannot unambiguously be classified as either core or power-law galaxies, and which have central cusp slopes and absolute magnitudes intermediate between those of core and power-law galaxies.

Milos Milosavljevic and David Merritt investigated in collaboration with me and  Frank van den Bosch the influence of galaxy mergers on the properties of galactic cores, in particular on the slope of the surface brightness profile.
 

SN color evolution

I have participated in the investigation of (V-Near-Infrared) color evolution of type Ia SN as a tool to improve the determination of dust extinction in SN (Krisciunas et al., see here and here). The correction for dust extinction in SN lightcurves is essential if the SN are used as standard candles to determine extragalactic distances.
 

Seeing Monitor (Dimm)

The APO Differential Image Motion Monitor (DIMM) was built by Armin Rest and Chris Stubbs from UW. This device samples the differential image motion of a single bright star between two separate optical paths through the atmosphere. This is accomplished with a 10'' telescope, which has a two-aperture mask on the front and a prism which displaces the light from one aperture to produce two well-separated subimages of one and the same star onto a single CCD camera. Wavefront perturbations caused by turbulence in the atmosphere (commonly denoted as seeing) cause relative motion of the two subimages, but common mode motion, such as tracking errors and wind shakes, affect each image in the same manner and do not introduce relative image motion. Therefore the variation of the subimage separation is an excellent way of obtaining a quantitative estimate of the seeing. The idea of the DIMM seeing monitor was adopted from the ESO Dimm sytem developed by M. Sarazin and F. Roddier (Sarazin, M., Roddier, F., "The ESO differential image motion monitor", 1990, Astron. Astrophy.227, 294-300). For more information check out my Dimm webpage or the AAS'01 poster.
 

Properties of CCD Detectors

With my old group from Portland State University (Erik Bodegom, Ralf Widenhorn, Lars Muendermann & Tom McGlinn), we investigate the properties of CCD detectors. One of our first projects was to characterize residual images in CCD detectors: Impurity sites in the bulk of the silicon get filled by photoexcitation. The subsequent slow release into the conduction band produces the residual images. We experimentally derive values for the cross section, density, and characteristic energy of the impurity sites responsible for the residual images. In another project, the durck current in CCDs is used to test the Meyer-Neldel rule. We find that the Meyer-Neldel rule arises naturally for a quantity where both an intrinsic process as well as a process involving impurities contribute (for more details see papers here and here). Here I would like to thank my dear friend and collaborator Tom McGlinn, who deceased in a tragic accident in 1998. He was and has been an inspiration to me with his fantastic humor and his love of life. It was a true privilige to know him, to have a friend like him.