arXiv subjects

Dana Koeppe

Publications and source records attributed to Dana Koeppe.

4 recordsLinked to original sources

arXiv2026

Operational capabilities and on-sky performance of SAMOS at the completion of science commissioning

We present the operational capabilities and on-sky performance of the SOAR Adaptive Module Optical Spectrograph (SAMOS) at the completion of its science commissioning phase. SAMOS is a Digital Micromirror Device (DMD)-based multi-object spectrograph and imager installed behind the SOAR Adaptive Module (SAM) ground-layer adaptive optics system. The instrument relays the full 3 x 3 arcmin AO-corrected field onto a large-format DMD, where each micromirror can direct light to either a spectroscopic or a parallel imaging channel. This architecture enables programmable slit-mask patterns that can be generated and reconfigured within seconds. SAMOS provides low-resolution spectroscopy over the 4000-10000 A wavelength range at resolving power R ~ 2500 and high-resolution spectroscopy (R ~ 10,000) in the 4500-5150 A and 6 000-7000 A bands. We summarize the operational workflow established during commissioning, including target acquisition, astrometric registration, DMD slit-mask generation, simultaneous imaging and spectroscopy, and automated data reduction. Science-verification observations demonstrate accurate target acquisition, reliable programmable slit-mask operation, multiplexed spectroscopy of crowded stellar fields, wavelength-calibration accuracy of about 0.3 A, and end-to-end spectrophotometric calibration through the combination of imaging and spectroscopic data. These results establish SAMOS as a unique facility instrument that combines adaptive-optics-assisted imaging, programmable multi-object spectroscopy, and rapid slit-mask reconfiguration for efficient spectroscopic surveys, transient follow-up, and studies of crowded stellar populations.

astro-ph.IM↗

arXiv2023

A HST Study of the Substellar Population of NGC 2024

We performed a HST/WFC3-IR imaging survey of the young stellar cluster NGC 2024 in three filters probing the 1.4~$μ$m H$_2$O absorption feature, characteristic of the population of low mass and sub-stellar mass objects down to a few Jupyter masses. We detect 812 point sources, 550 of them in all 3 filters with signal to noise greater than 5. Using a distance-independent two-color diagram we determine extinction values as high as $A_V\simeq 40$. We also find that the change of effective wavelengths in our filters results in higher $A_V$ values as the reddening increases. Reconstructing a dereddened color-magnitude diagram we derive a luminosity histogram for both the full sample of candidate cluster members and for an extinction-limited sub-sample containing the 50% of sources with $A_V\lesssim 15$. Assuming a standard extinction law like Cardelli et al. (1989) with a nominal $R_V$=3.1 we produce a luminosity function in good agreement with the one resulting from a Salpeter-like Initial Mass Function for a 1~Myr isochrone. There is some evidence of an excess of luminous stars in the most embedded region. We posit that the correlation may be due to those sources being younger, and therefore overluminous than the more evolved and less extinct cluster's stars. We compare our classification scheme based on the depth of the 1.4$μ$m photometric feature with the results from the spectroscopic survey of Levine et al. (2006), and we report a few peculiar sources and morphological features typical of the rich phenomenology commonly encountered in young star-forming regions.

astro-ph.GA↗

arXiv2020

Clusters of Galaxies Masquerading as X-Ray Quasars

Inspired by the discovery of the Phoenix cluster by the South Pole Telescope team, we initiated a search for other massive clusters of galaxies missing from the standard X-ray catalogs. We began by identifying 25 cluster candidates not included in the Meta-Catalog of X-ray Clusters of galaxies cluster compilation through cross-identification of the central galaxies of optically identified clusters in the Sloan Digital Sky Survey GMBCG catalog with bright X-ray sources in the ROSAT Bright Source Catalog. Those candidates were mostly unidentified or previously classified as X-ray active galactic nucleus (AGN). We analyzed brief Chandra X-ray Observatory observations of 14 of these X-ray sources and found that eight are X-ray luminous clusters of galaxies, only one showing evidence for a central X-ray point source. The remaining six candidates turned out to be point-source dominated, with faint detections or upper limits on any extended emission. We were not able to rule out the presence of extended X-ray emission from any of the point sources. The levels of extended emission around the six point sources are consistent with expectations based on optical richness, but could also be contaminated by scattered X-ray light from the central point source or extended nonthermal emission from possible radio lobes. We characterize the extended components of each of the well-detected cluster sources, finding that six of the eight X-ray clusters are consistent with being compact cool-core clusters. One of the newly identified low-luminosity X-ray clusters may have had an X-ray-luminous AGN 20 yr prior to the recent Chandra observations, based on the 4σ difference between its Chandra and ROSAT fluxes.

astro-ph.GA↗

arXiv2015

1FGL J1417.7-4407: A likely gamma-ray bright binary with a massive neutron star and a giant secondary

We present multiwavelength observations of the persistent Fermi-LAT unidentified gamma-ray source 1FGL J1417.7-4407, showing it is likely to be associated with a newly discovered X-ray binary containing a massive neutron star (nearly 2 M_sun) and a ~ 0.35 M_sun giant secondary with a 5.4 day period. SOAR optical spectroscopy at a range of orbital phases reveals variable double-peaked H-alpha emission, consistent with the presence of an accretion disk. The lack of radio emission and evidence for a disk suggests the gamma-ray emission is unlikely to originate in a pulsar magnetosphere, but could instead be associated with a pulsar wind, relativistic jet, or could be due to synchrotron self-Compton at the disk--magnetosphere boundary. Assuming a wind or jet, the high ratio of gamma-ray to X-ray luminosity (~ 20) suggests efficient production of gamma-rays, perhaps due to the giant companion. The system appears to be a low-mass X-ray binary that has not yet completed the pulsar recycling process. This system is a good candidate to monitor for a future transition between accretion-powered and rotational-powered states, but in the context of a giant secondary.

astro-ph.HE↗