M. H. Siegel
A5042608090- Gamma-ray bursts and supernovae
- Astronomical Observations and Instrumentation
- SAS software applications and methods
- Astronomy and Astrophysical Research
- Stellar, planetary, and galactic studies
- Astrophysical Phenomena and Observations
- Astrophysics and Star Formation Studies
- Pulsars and Gravitational Waves Research
- Galaxies: Formation, Evolution, Phenomena
- Adaptive optics and wavefront sensing
- Astrophysics and Cosmic Phenomena
- Geophysics and Gravity Measurements
- History and Developments in Astronomy
- Color perception and design
- Astro and Planetary Science
- Color Science and Applications
- Visual perception and processing mechanisms
- Inertial Sensor and Navigation
- Calibration and Measurement Techniques
- Statistical and numerical algorithms
- Radio Astronomy Observations and Technology
- COVID-19 diagnosis using AI
- Solar and Space Plasma Dynamics
- Atmospheric Ozone and Climate
- Space Exploration and Technology
Tufts University
2025
Pennsylvania State University
2015-2024
University of Illinois Chicago
2022-2024
Oregon Dermatology & Research Center
2023-2024
University of Illinois Urbana-Champaign
2023
Indo-American Center
2023
Las Cumbres Observatory Global Telescope Network
2016-2021
Glaucoma Research Foundation
2020
Oakland University
2020
Yale University
1989-2018
We present the first results of a large Advanced Camera for Surveys (ACS) survey Galactic globular clusters. This Hubble Space Telescope (HST) Treasury project is designed to obtain photometry with S/N (signal-to-noise ratio) ≳10 main-sequence stars masses ≳0.2 M⊙ in sample globulars using ACS Wide Field Channel. Here we focus on clusters without previous HST imaging data. These include NGC 5466, 6779, 5053, 6144, Palomar 2, E3, Lyngå 7, 1, and 6366. Our color-magnitude diagrams (CMDs)...
Context. The fraction of binary stars is an important ingredient to interpret globular cluster dynamical evolution and their stellar population.
The ACS Survey of Globular Clusters has used HST's Wide-Field Channel to obtain uniform imaging 65 the nearest globular clusters provide an extensive homogeneous dataset for a broad range scientific investigations. survey goals required not only observing strategy, but also reduction strategy. To this end, we designed sophisticated software program process cluster data in automated way. identifies stars simultaneously multiple dithered exposures each and measures them using best available...
The ACS Survey of Galactic Globular Clusters is a Hubble Space Telescope (HST) Treasury program designed to provide new large, deep and homogeneous photometric database. Based on observations from this program, we have measured precise relative ages for sample 64 globular clusters by comparing the position clusters' main sequence turn offs, using main-sequence fitting cross-compare within sample. This method provides formal precision 2-7%. We demonstrate that calculated are independent...
The horizontal branch (HB) morphology of globular clusters (GCs) is most strongly influenced by metallicity. second parameter phenomenon, first described in the 1960s, acknowledges that metallicity alone not enough to describe HB all GCs. In particular, astronomers noticed outer Galactic halo contains GCs with redder HBs at a given than are found inside solar circle. Thus, least was required characterize morphology. While term "second parameter" has since come be used broader context, its...
With the first direct detection of merging black holes in 2015, era gravitational wave (GW) astrophysics began. A complete picture compact object mergers, however, requires an electromagnetic (EM) counterpart. We report ultraviolet (UV) and X-ray observations by Swift Nuclear Spectroscopic Telescope ARray (NuSTAR) EM counterpart binary neutron star merger GW170817. The bright, rapidly fading emission indicates a high mass ($\approx0.03$ solar masses) wind-driven outflow with moderate...
We report the discovery of unusually bright long-duration gamma-ray burst (GRB), GRB 221009A, as observed by Neil Gehrels Swift Observatory (Swift), Monitor All-sky X-ray Image (MAXI), and Neutron Star Interior Composition Explorer Mission (NICER). This energetic was located relatively nearby (z = 0.151), allowing for sustained observations afterglow. The large luminosity low Galactic latitude (b 4.3 degrees) make 221009A a powerful probe dust in Milky Way. Using echo tomography we map...
Photometry with the Hubble Space Telescope Advanced Camera for Surveys (HST ACS) reveals that subgiant branch (SGB) of globular cluster NGC 1851 splits into two well-defined branches. If split is due only to an age effect, SGBs would imply star formation episodes separated by ~1 Gyr. We discuss other anomalies in could be interpreted terms a double stellar population. Finally, we compare case globulars known host multiple populations, and show all three clusters differ several important respects.
The Ultraviolet/Optical Telescope (UVOT) is one of three instruments onboard the Swift observatory. photometric calibration has been published, and this paper follows up with details on other aspects including a measurement point spread function an assessment orbital variation effect photometry. A correction for large-scale variations in sensitivity over field view described, as well model coincidence loss which used to assess extended regions. We have provided detector distortion measured...
In an effort to more precisely define the spatial distribution of Galactic field stars, we present analysis photometric parallaxes 70,000 stars covering nearly 15 square degrees in seven Kapteyn Selected Areas. We address affects Malmquist Bias, subgiant/giant contamination, metallicity and binary upon derived density laws. The affect is most significant. find that while disk-like populations Milky Way are easily constrained a simultaneous all fields, no good solution for halo found. have...
As part of the ACS Survey Galactic Globular Clusters, we present new Hubble Space Telescope photometry massive globular cluster M54 (NGC 6715) and superposed core tidally disrupted Sagittarius (Sgr) dSph galaxy. Our deep (F606W ~ 26.5), high-precision yields an unprecedentedly detailed color-magnitude diagram showing extended blue horizontal branch multiple main sequences M54+Sgr system. The distance reddening to are revised using both isochrone main-sequence fitting (m - M)0 = 17.27 E(B V)...
We present a catalog of Fe, Mg, Si, Ca, and Ti abundances for 2961 stars in eight dwarf satellite galaxies the Milky Way (MW): Sculptor, Fornax, Leo I, Sextans, II, Canes Venatici Ursa Minor, Draco. For purposes validating our measurements, we also observed 445 red giants MW globular clusters 21 field halo. The measurements are based on Keck/DEIMOS medium-resolution spectroscopy (MRS) combined with spectral synthesis. estimate uncertainties [Fe/H] by quantifying dispersion sample...
Recent intensive Swift monitoring of the Seyfert 1 galaxy NGC 5548 yielded 282 usable epochs over 125 days across six UV/optical bands and X-rays. This is densest extended AGN continuum sampling ever obtained, with a mean rate <0.5 day. Approximately daily HST UV was also obtained. The light curves show strong correlations (r_max = 0.57 - 0.90) clearest measurement to date interband lags. These lags are well-fit by \tau propto \lambda^4/3 wavelength dependence, normalization that indicates...
ABSTRACT We present ground-based optical photometric monitoring data for NGC 5548, part of an extended multiwavelength reverberation mapping campaign. The light curves have nearly daily cadence from 2014 January to July in nine filters ( BVRI and ugriz ). Combined with ultraviolet the Hubble Space Telescope Swift , we confirm significant time delays between continuum bands as a function wavelength, extending wavelength coverage 1158 Å z band (~9160 Å). find that lags at wavelengths longer...
We describe the first results from a six-month long reverberation-mapping experiment in ultraviolet based on 170 observations of Seyfert 1 galaxy NGC 5548 with Cosmic Origins Spectrograph Hubble Space Telescope. Significant correlated variability is found continuum and broad emission lines, amplitudes ranging ~30% to factor two lines three continuum. The variations all strong lag behind those continuum, He II 1640 lagging by ~2.5 days Lyman alpha 1215, C IV 1550, Si 1400 ~5-6 days....
The bright transient AT2018cow has been unlike any other known type of transient. Its high brightness, rapid rise and decay initially nearly featureless spectrum are unprecedented difficult to explain using models for similar burst sources. We present evidence faint gamma-ray emission continuing at least 8 days, spectra in the ultraviolet bands -- both unusual eruptive X-ray variability source a burst-like character. UV-optical does not show CNO line but is well described by blackbody....
The IceCube report of a $\sim 3.5σ$ excess $13\pm5$ neutrino events in the direction blazar TXS 05056+056 2014-2015 and 2017 detection high-energy neutrino, IceCube-170922A, during gamma-ray flare from same blazar, have revived interest scenarios for production blazars. We perform comprehensive analyses on long-term electromagnetic emission using optical, X-ray, data All-Sky Automated Survey Supernovae (ASAS-SN), Neil Gehrels Swift Observatory (Swift), Monitor All-sky X-ray Image (MAXI),...
Evidence-based recommendations for the treatment of vitiligo in pediatric, adolescent, and young adult patients US are needed.
We analyze velocity dispersion profiles for the Draco and Ursa Minor (UMi) dwarf spheroidal (dSph) galaxies based on published new Keck HIRES spectra stars in outer UMi field. Washington + DDO51 filter photometric catalogs provide additional leverage membership of individual and, beyond 0.5 King limiting radii (rlim), identify bona fide dSph members up to 4.5 times more efficiently than simple color-magnitude diagram selections. Previously reported "cold populations" at rlim are not obvious...
We have used observations obtained as part of the Hubble Space Telescope/ACS Survey Galactic Globular Clusters to construct global present-day mass functions for 17 globular clusters utilizing multi-mass King models extrapolate from our cluster behavior. The these are well matched by power laws turnoff, ≈0.8 M☉, 0.2–0.3 M☉ on lower main sequence. slopes those power-law fits, α, been correlated with an extensive set intrinsic and extrinsic properties investigate which parameters may influence...
We present the earliest ultraviolet (UV) observations of bright Type Ia supernova SN 2011fe/PTF11kly in nearby galaxy M101 at a distance only 6.4 Mpc. It was discovered shortly after explosion by Palomar Transient Factory and first observed Swift/UVOT about day explosion. The early UV light is well-defined, with ~20 data points per filter five days These well-sampled form new template curves for comparison other SNe low high redshift. report fits from semi-empirical models find time...