A5013708068- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astronomical Observations and Instrumentation
- Solar and Space Plasma Dynamics
- Astrophysical Phenomena and Observations
- Astro and Planetary Science
- Gamma-ray bursts and supernovae
- Astrophysics and Star Formation Studies
- Calibration and Measurement Techniques
- Particle physics theoretical and experimental studies
- Statistical and numerical algorithms
- High-Energy Particle Collisions Research
- Quantum Chromodynamics and Particle Interactions
- Adaptive optics and wavefront sensing
- Galaxies: Formation, Evolution, Phenomena
- Astrophysics and Cosmic Phenomena
- Scientific Measurement and Uncertainty Evaluation
- Particle Detector Development and Performance
- Medical Imaging Techniques and Applications
- Nuclear Physics and Applications
- CCD and CMOS Imaging Sensors
- Geophysics and Gravity Measurements
- Ionosphere and magnetosphere dynamics
- Pulsars and Gravitational Waves Research
- Image and Signal Denoising Methods
Homi Bhabha National Institute
2022-2024
Center for Astrophysics Harvard & Smithsonian
2015-2024
Intel (United States)
2017-2024
National Institute of Science Education and Research
2022-2024
Smithsonian Astrophysical Observatory
2012-2023
University of Houston
2023
European Organization for Nuclear Research
2023
University College London
2022
Southwest Research Institute
2022
Harvard University Press
2002-2017
The likelihood ratio test (LRT) and the related $F$ test, do not (even asymptotically) adhere to their nominal $\chi^2$ distributions in many statistical tests common astrophysics, thereby casting marginal line or source detections non-detections into doubt. Although there are legitimate uses of these statistics, some important cases it can be impossible compute correct false positive rate. For example, has become practice use LRT for detecting a spectral model above background despite lack...
Wavelets are scalable, oscillatory functions that deviate from zero only within a limited spatial regime and have average value zero, thus may be used to simultaneously characterize the shape, location, strength of astronomical sources. But in addition their use as source characterizers, wavelet rapidly gaining currency detection field. Wavelet-based involves correlation scaled with binned, two-dimensional image data. If chosen function exhibits property vanishing moments, significantly...
The Chandra Source Catalog (CSC) is a general purpose virtual X-ray astrophysics facility that provides access to carefully selected set of generally useful quantities for individual sources, and designed satisfy the needs broad-based group scientists, including those who may be less familiar with astronomical data analysis in regime. first release CSC includes information about 94,676 distinct sources detected subset public ACIS imaging observations from roughly eight years mission. This...
A commonly used measure to summarize the nature of a photon spectrum is so-called hardness ratio, which compares numbers counts observed in different passbands. The ratio especially useful distinguish between and categorize weak sources as proxy for detailed spectral fitting. However, this regime classical methods error propagation fail, estimates become unreliable. Here we develop rigorous statistical treatment ratios that properly deals with detected photons independent Poisson random...
\textit{Extreme Ultraviolet Explorer} Deep Survey observations of cool stars (spectral type F to M) have been used investigate the distribution coronal flare rates in energy and its relation activity indicators rotation parameters. Cumulative differential rate distributions were constructed fitted with different methods. Power laws are found approximately describe distributions. A trend toward flatter for later-type is suggested our sample. Assuming that power continue below detection limit,...
Deep Chandra Low Energy Transmission Grating and High Resolution Camera spectroscopic observations of the isolated neutron star candidate RX J1856.5-3754 have been analyzed to search for metallic resonance cyclotron spectral features pulsation behavior. As found from earlier observations, X-ray spectrum is well represented by an ~60 eV (7 × 105 K) blackbody. No unequivocal evidence line or edge has found, arguing against metal-dominated models. The data contain no pulsation, we place a 99%...
We carry out the first time-dependent numerical MagnetoHydroDynamic modeling of an extrasolar planetary system to study interaction stellar magnetic field and wind with magnetosphere outflow. base our model on parameters HD 189733 system, which harbors a close-in giant planet. Our simulation reveals highly structured corona characterized by sectors different plasma properties. The star-planet varies in magnitude complexity, depending phase, strength, relative orientation fields. It also...
The Large Synoptic Survey Telescope is designed to provide an unprecedented optical imaging dataset that will support investigations of our Solar System, Galaxy and Universe, across half the sky over ten years repeated observation. However, exactly how LSST observations be taken (the observing strategy or "cadence") not yet finalized. In this dynamically-evolving community white paper, we explore detailed performance anticipated science expected depend on small changes strategy. Using...
We present the results of first strong lens time delay challenge. The motivation, experimental design, and entry level challenge are described in a companion paper. This paper presents main challenge, TDC1, which consisted analyzing thousands simulated light curves blindly. observational properties cover range quality obtained for current targeted efforts (e.g., COSMOGRAIL) expected from future synoptic surveys LSST), include systematic errors. Seven teams participated submitting 78...
Stars of stellar type later than about M3.5 are believed to be fully convective and therefore unable support magnetic dynamos like the one that produces 11-year solar cycle. Because their intrinsic faintness, very few late M stars have undergone long-term monitoring test this prediction, which is critical our understanding field generation in such stars. Magnetic activity also interest as driver UV X-ray radiation, well energetic particles winds, affect atmospheres close-in planets lie...
We have developed a new method for the reconstruction of differential emission measure distributions based on Metropolis Markov-chain Monte Carlo (MCMC[M]) method. This technique allows us to (1) relax nonphysical smoothness constraints generally imposed DEMs, (2) determine confidence bounds computed values, and (3) include extra information in form upper limits. Using MCMC[M] algorithm, we reanalyze extreme ultraviolet spectral line fluxes obtained from Solar Extreme Ultraviolet Rocket...
We present the first X-ray spectrum obtained by Low-Energy Transmission Grating Spectrometer (LETGS) aboard Chandra X-Ray Observatory. The is of Capella and covers a wavelength range 5-175 Å (2.5-0.07 keV). measured resolution, which in good agreement with ground calibration, Deltalambda approximately 0.06 (FWHM). Although in-flight calibration LETGS progress, high spectral resolution unique coverage are well demonstrated results from Capella, coronal source rich emission lines. While...
We present the Chandra Multiwavelength Project (ChaMP) X-ray point source catalog with ~6800 sources detected in 149 observations covering ~10 deg2. The full ChaMP sample is 7 times larger than initial published catalog. exposure time of fields our ranges from 0.9 to 124 ks, corresponding a deepest flux limit f0.5-8.0 = 9 × 10-16 ergs cm-2 s-1. data have been uniformly reduced and analyzed ChaMP-specific pipelines then carefully validated by visual inspection. includes photometric eight...
The frequency of heating events in the corona is an important constraint on coronal mechanisms. Observations indicate that intensities and velocities measured active region cores are effectively steady, suggesting occur rapidly enough to keep high temperature loops close equilibrium. In this paper, we couple observations Active Region 10955 made with XRT EIS \textit{Hinode} test a simple steady model. First calculate differential emission measure apex core. We find DEM be broad peaked around...
The X-Ray Telescope (XRT) on the Japanese/USA/UK Hinode (Solar-B) spacecraft has detected emission from a quiescent active region core that is consistent with nanoflare heating. fluxes 10 broadband X-ray filters and filter combinations were used to construct differential measure (DEM) curves. In addition expected peak at log T = 6.3–6.5, we find high-temperature component significant > 7.0. This weak compared main peak—the DEM down by almost three orders of magnitude—which accounts fact it...
Testing whether close-in massive exoplanets (hot Jupiters) can enhance the stellar activity in their host primary is crucial for models of and planetary evolution. Among systems with hot Jupiters, HD 189733 one best studied because its proximity, strong activity, presence a transiting planet, which allows transmission spectroscopy measure radius density. Here we report on X-ray star, A, using new XMM-Newton observation comparison previous observations. The spectrum quiescent intervals...
Abstract We report on the X-ray spectral and spatial evolution of symbiotic star R Aqr. Through a multiepoch observational campaign performed with Chandra between 2017 2022, we study emission this binary system, composed an evolved red giant white dwarf (WD). This analysis is particularly timely as WD approached periastron in late 2018/early 2019; thus, mass transfer, jet emission, outburst phenomena are to be expected. detailed analysis, detect significant rise soft (0.5–2 keV) Aqr, likely...
We investigate the EUV and X-ray flare rate distribution in radiated energy of late-type active star AD Leo.Occurrence rates solar flares have previously been found to be distributed according a power law, dN=dE / E À , with power-law index range 1.5-2.6.If ! 2, then an extrapolation low energies may sufficient heat complete observable X-ray/EUV corona.We obtained long observations Leo EUVE BeppoSAX satellites.Numerous detected, ranging over almost 2 orders magnitude their energy.We compare...
The Chandra Multi-wavelength Project (ChaMP) is a wide-area (~14 deg^2) survey of serendipitous X-ray sources, aiming to establish fair statistical samples covering wide range characteristics (such as absorbed AGNs, high z clusters galaxies) at flux levels (fX ~ 10^-15 - 10^-14 erg sec-1 cm-2) intermediate between the Deep surveys and previous missions. We present first ChaMP catalog, which consists 991 near on-axis, bright sources obtained from initial sample 62 observations. data have been...
view Abstract Citations (114) References (81) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Coronae of Low-Mass Dwarf Stars Giampapa, M. S. ; Rosner, R. Kashyap, V. Fleming, T. A. Schmitt, J. H. Bookbinder, We report the results our analysis pointed X-ray observations nearby dMe and dM stars using position sensitive proportional counter (PSPC) on board ROSA T satellite (Roentgensatellit). In cases those M dwarf where PSPC pulse-height distributions...
We have carried out a survey of X-ray emission from stars with giant planets, combining both archival and targeted surveys. Over 230 been currently identified as possessing roughly third these detected in X-rays. carry detailed statistical analysis on volume limited sample main sequence star systems comparing subsamples that close-in planets more distant planets. This reveals strong evidence are average active by factor ~4 than those distant. result persists for various selections. find even...
We report on two XMM-Newton observations of the planetary host star HD 189733. The system has a close in planet and it can potentially affect coronal structure via interactions with magnetosphere. have obtained X-ray spectra light curves from EPIC Reflection Grating Spectrometer board which we analyzed interpreted. reduced data primary transit secondary eclipse that occurred 2007 April 17 2009 May 18, respectively. In observation, only variability due to weak flares is recognized. 189733...
Since the first discovery of an extrasolar planetary system more than a decade ago, hundreds have been discovered. Surprisingly, many these systems harbor Jupiter-class gas giants located close to central star, at distances 0.1 AU or less. Observations chromospheric 'hot spots' that rotate in phase with orbit, and elevated stellar X-ray luminosities,suggest close-in planets significantly affect structure outer atmosphere star through interactions between magnetic field magnetosphere. Here we...
We present a numerical Magnetohydrodynamic (MHD) study of the dependence stellar mass and angular momentum- loss rates on orbital distance to close-in giant planets. find that rate drops by factor $\approx$1.5-2, while momentum $\approx$4 as decreases past Alfv\'en surface. This reduction in is due interaction between planetary surfaces, which modifies global structure corona wind hemisphere facing planet, well opposite hemisphere. The simulation also shows magnitude change depends mostly...