arXiv subjects

K. V. Getman

Publications and source records attributed to K. V. Getman.

15 recordsLinked to original sources

arXiv2026

Exploring Space Weather From Young Solar-like Stars as Windows to Exoplanetary Habitability

Young solar-like stars are efficient generators of magnetic activity, superflares, coronal mass ejections (CMEs), and stellar energetic particles. These phenomena drive the early evolution of stars and shape the habitability of exoplanets. The Hubble Space Telescope (HST), with its unmatched far-ultraviolet (FUV) and near-ultraviolet (NUV) sensitivity, provides a uniquely powerful window into these processes one that no current or near future facility can replicate. This white paper articulates four interconnected science questions that require Hubble continued operation and targeted observing programs over the next 10 to 15 years, enriched by new multi-wavelength insights from deep X-ray surveys of open clusters. We describe required instrument capabilities, critical synergies with contemporaneous missions (JWST, Chandra, XMM Newton, TESS, and the Nancy Grace Roman Space Telescope), and the fundamental role Hubble observations will play in calibrating and informing the design of the Habitable Worlds Observatory (HWO). We advocate for large scale coordinated campaigns targeting young solar-like stars as the highest priority science program for the coming decade.

astro-ph.IM↗

arXiv2025

Time-resolved protoplanetary disk physics in DQ Tau with JWST

Accretion variability is ubiquitous in YSOs. While large outbursts may strongly affect the disk, the effects of moderate bursts are less understood. We aim to study the physical response of the disk around the eccentric binary system DQ Tau to its periodic accretion changes. We organized a multi-wavelength campaign centered on four JWST/MIRI spectra. We targeted three periastrons (high accretion state) and one apastron (quiescence). We used optical and near-infrared spectroscopy and photometry to measure how the accretion luminosity varies. We decomposed the multi-epoch SEDs into stellar, accretion, and rim components. We fitted the solid-state features using various opacity curves and the molecular features using slab models. We find the inner disk of DQ Tau to be highly dynamic. The temperature, luminosity, and location of the inner dust rim vary in response to the movement of stars and the L_acc variations. This causes variable shadowing of the outer disk, leading to an anti-correlation between the rim temperature and the strength of the silicate feature. The dust mineralogy remains constant, dominated by large amorphous olivine and pyroxene grains, with smaller fractions of crystalline forsterite. The excitation of CO (1550-2260 K), HCN (880-980 K), and hot H2O (740-860 K) molecules as well as the luminosity of the [NeII] line correlate with the accretion rate, while the warm (650 K) and cold (170-200 K) H2O components are mostly constant. CO emission, originating from a hot (>1500 K) region likely within the dust sublimation radius, is most sensitive to L_acc changes. In comparison with other T Tauri disks, DQ Tau is highly C-poor and displays moderately inefficient pebble drift. We conclude that even moderate accretion rate changes affect the thermal structure in the planet-forming disk regions on short timescales, providing a crucial benchmark for understanding disk evolution.

astro-ph.SR↗

arXiv2019

Gaia Stellar Kinematics in the Head of the Orion A Cloud: Runaway Stellar Groups and Gravitational Infall

This work extends previous kinematic studies of young stars in the Head of the Orion A cloud (OMC-1/2/3/4/5). It is based on large samples of infrared, optical, and X-ray selected pre-main sequence stars with reliable radial velocities and Gaia-derived parallaxes and proper motions. Stellar kinematic groups are identified assuming they mimic the motion of their parental gas. Several groups are found to have peculiar kinematics: the NGC 1977 cluster and two stellar groups in the Extended Orion Nebula (EON) cavity are caught in the act of departing their birthplaces. The abnormal motion of NGC 1977 may have been caused by a global hierarchical cloud collapse, feedback by massive Ori OB1ab stars, supersonic turbulence, cloud-cloud collision, and/or slingshot effect; the former two models are favored by us. EON groups might have inherited anomalous motions of their parental cloudlets due to small-scale `rocket effects' from nearby OB stars. We also identify sparse stellar groups to the east and west of Orion A that are drifting from the central region, possibly a slowly expanding halo of the Orion Nebula Cluster. We confirm previously reported findings of varying line-of-sight distances to different parts of the cloud's Head with associated differences in gas velocity. Three-dimensional movies of star kinematics show contraction of the groups of stars in OMC-1 and global contraction of OMC-123 stars. Overall, the Head of Orion A region exhibits complex motions consistent with theoretical models involving hierarchical gravitational collapse in (possibly turbulent) clouds with OB stellar feedback.

astro-ph.GA↗

arXiv2012

Splinter Session "Solar and Stellar Flares"

This summary reports on papers presented at the Cool Stars-16 meeting in the splinter session "Solar and Stellar flares." Although many topics were discussed, the main themes were the commonality of interests, and of physics, between the solar and stellar flare communities, and the opportunities for important new observations in the near future.

astro-ph.SR↗

arXiv2011

The Soft X-ray Lightcurves of Partially Eclipsed Stellar Flares

Most stellar flares' soft X-ray lightcurves possess a `typical' morphology, which consists of a rapid rise followed by a slow exponential decay. However, a study of 216 of the brightest flares on 161 pre-main sequence stars, observed during the Chandra Orion-Ultradeep Project (COUP), showed that many flare lightcurves depart from this typical morphology. While this can be attributed to the superposition of multiple typical flares, we explore the possibility that the time-variable eclipsing of flares by their host stars may also be an important factor. We assume each flare is contained within a single, uniform plasma density magnetic loop and specify the intrinsic variation of the flare's emission measure with time. We consider rotational eclipse by the star itself, but also by circumstellar discs and flare-associated prominences. Based on this simple model, we generate a set of flares similar to those observed in the COUP database. Many eclipses simply reduce the flare's maximum emission measure or decay time. We conclude therefore that eclipses often pass undetected, but usually have only a modest influence on the flare emission measure profile and hence the derived loop lengths. We show that eclipsing can easily reproduce the observed atypical flare morphologies. The number of atypical modelled flare morphologies is however much less than that found in the COUP sample. The large number of observed atypical flare morphologies, therefore, must be attributed to other processes such as multiple flaring loops.

astro-ph.SR↗

arXiv2011

Variable X-ray emission from the accretion shock in the Classical T Tauri Star V2129 Oph

The soft X-ray emission from high density plasma in CTTS is associated with the accretion process. It is still unclear whether this high density cool plasma is heated in the accretion shock, or if it is coronal plasma fed/modified by the accretion process. We conducted a coordinated quasi-simultaneous optical and X-ray observing campaign of the CTTS V2129 Oph (Chandra/HETGS data to constrain the X-ray emitting plasma components, and optical observations to constrain the characteristics of accretion and magnetic field). We analyze a 200 ks Chandra/HETGS observation of V2129 Oph, subdivided into two 100 ks segments, corresponding to two different phases within one stellar rotation. The X-ray emitting plasma covers a wide range of temperatures: 2-34 MK. The cool plasma component of V2129 Oph varies between the two segments of the Chandra observation: high density plasma (log Ne ~ 12.1) with high EM at ~ 3-4 MK is present during the 1st segment; during the 2nd segment this plasma component has lower EM and lower density (log Ne < 11.5), although the statistical significance of these differences is marginal. Hotter plasma components, T > 10 MK, show variability on short time scales (~ 10 ks), typical of coronal plasma. A clear flare, detected in the 1st segment, could be located in a large coronal loop (> 3 Rstar). Our observation provides further confirmation that the dense cool plasma at a few MK in CTTS is material heated in the accretion shock. The variability of this cool plasma component on V2129 Oph may be explained in terms of X-rays emitted in the accretion shock and seen with different viewing angles at the two rotational phases probed by our observation. During the 1st time interval direct view of the shock region is possible, while, during the 2nd, the accretion funnel itself intersects the line of sight to the shock region, preventing us from observing accretion-driven X-rays.

astro-ph.SR↗

arXiv2010

Recurring millimeter flares as evidence for star-star magnetic reconnection events in the DQ Tauri PMS binary system

Observations of the T Tauri spectroscopic binary DQ Tau in April 2008 captured an unusual flare at 3 mm, which peaked at an observed max flux of 0.5 Jy (about 27x the quiescent value). Here we present follow-up mm observations that demonstrate a periodicity to the phenomenon. While monitoring 3 new periastron encounters, we detect flares within 17.5 hrs (or 4.6%) of the orbital phase of the first reported flare, and we constrain the main emitting region to a stellar height of 3.7-6.8 Rstar. The recorded activity is consistent with the proposed picture for synchrotron emission initiated by a magnetic reconnection event when the two stellar magnetospheres of the highly eccentric (e=0.556) binary are believed to collide near periastron as the stars approach a minimum separation of 8 Rstar (~13 Rsolar). The similar light curve decay profiles allow us to estimate an average flare duration of 30 hrs. Assuming one mm flare per orbit, DQ Tau could spend approximately 8% of its 15.8-d orbital period in an elevated flux state. Our analysis of the mm emission provides an upper limit of 5% on the linear polarization. We discuss the extent to which a severely entangled magnetic field structure and Faraday rotation effects are likely to reduce the observed polarization fraction. We also predict that, for the current picture, the stellar magnetospheres must be misaligned at a significant angle or, alternatively, that the topologies of the outer magnetospheres are poorly described by a well-ordered dipole inside a radius of 7 Rstar. Finally, to investigate whether reorganization of the magnetic field during the interaction affects mass accretion, we also present simultaneous optical (VRI) monitoring, as an established tracer of accretion activity in this system. We find that an accretion event can occur coincident in both time and duration with the synchrotron fallout of a magnetic reconnection event.

astro-ph.SR↗

arXiv2009

Multi-wavelength observing of a forming solar-like star

V2129 Oph is a 1.35 solar mass classical T Tauri star, known to possess a strong and complex magnetic field. By extrapolating from an observationally derived magnetic surface map, obtained through Zeeman-Doppler imaging, models of V2129 Oph's corona have been constructed, and used to make predictions regarding the global X-ray emission measure, the amount of modulation of X-ray emission, and the density of accretion shocks. In late June 2009 we will under take an ambitious multi-wavelength, multi-observing site, and near contemporaneous campaign, combining spectroscopic optical, nIR, UV, X-ray, spectropolarimetric and photometric monitoring. This will allow the validity of the 3D field topologies derived via field extrapolation to be determined.

astro-ph.SR↗

arXiv2007

An X-ray Imaging Study of the Stellar Population in RCW49

We present the results of a high-resolution X-ray imaging study of the stellar population in the Galactic massive star-forming region RCW49 and its central OB association Westerlund 2. We obtained a 40 ks X-ray image of a 17'x17' field using the Chandra X-ray Observatory and deep NIR images using the Infrared Survey Facility in a concentric 8'3x8'3 region. We detected 468 X-ray sources and identified optical, NIR, and Spitzer Space Telescope MIR counterparts for 379 of them. The unprecedented spatial resolution and sensitivity of the X-ray image, enhanced by optical and infrared imaging data, yielded the following results: (1) The central OB association Westerlund 2 is resolved for the first time in the X-ray band. X-ray emission is detected from all spectroscopically-identified early-type stars in this region. (2) Most (86%) X-ray sources with optical or infrared identifications are cluster members in comparison with a control field in the Galactic Plane. (3) A loose constraint (2--5 kpc) for the distance to RCW49 is derived from the mean X-ray luminosity of T Tauri stars. (4) The cluster X-ray population consists of low-mass pre--main-sequence and early-type stars as obtained from X-ray and NIR photometry. About 30 new OB star candidates are identified. (5) We estimate a cluster radius of 6'--7' based on the X-ray surface number density profiles. (6) A large fraction (90%) of cluster members are identified individually using complimentary X-ray and MIR excess emission. (7) The brightest five X-ray sources, two Wolf-Rayet stars and three O stars, have hard thermal spectra.

astro-ph↗

arXiv2007

Coronal Abundances in Orion Nebula Cluster Stars

Following the Chandra Orion Ultradeep Project (COUP) observation, we have studied the chemical composition of the hot plasma in a sample of 146 X-ray bright pre-main sequence stars in the Orion Nebula Cluster. We report measurements of individual element abundances for a subsample of 86 slightly-absorbed and bright X-ray sources, using low resolution X-ray spectra obtained from the Chandra ACIS instrument. The X-ray emission originates from a plasma with temperatures and elemental abundances very similar to those of active coronae in older stars. A clear pattern of abundances vs. First Ionization Potential (FIP) is evident if solar photospheric abundances are assumed as reference. The results are validated by extensive simulations. The observed abundance distributions are compatible with a single pattern of abundances for all stars, although a weak dependence on flare loop size may be present. The abundance of calcium is the only one which appears to vary substantially between stars, but this quantity is affected by relatively large uncertainties. The ensemble properties of the X-ray bright COUP sources confirm that the iron in the emitting plasma is underabundant with respect to both the solar composition and to the average stellar photospheric values. Comparison of the present plasma abundances with those of the stellar photospheres and those of the gaseous component of the nebula, indicates a good agreement for all the other elements with available measurements, and in particular for the high-FIP elements (Ne, Ar, O, and S) and for the low-FIP element Si. We conclude that there is evidence of a significant chemical fractionation effect only for iron, which appears to be depleted by a factor 1.5--3 with respect to the stellar composition.

astro-ph↗

arXiv2006

Hard X-rays from Ultra-Compact HII Regions in W49A

We report the Chandra detection of hard X-ray emission from the Welch ring in W49A, an organized structure of ultra-compact (UC) HII regions containing a dozen nascent early-type stars. Two UC HII regions are associated with hard X-ray emission in a deep Advanced CCD Imaging Spectrometer image exposed for 96.7 ks. One of the two X-ray sources has no near-infrared counterpart and is extended by ~5 arcsec, or ~0.3 pc, at a distance of ~11.4 kpc, which is spatially aligned with the cometary radio continuum emission associated with the UC HII region. The X-ray spectrum of the emission, when fit with a thermal model, indicates a heavily absorbed plasma with extinction of \~5x10^{23}/cm^{2}, temperature of ~7 keV, and X-ray luminosity in the 3.0-8.0 keV band of ~3x10^{33} ergs/s. Both the luminosity and the size of the emission resemble the extended hard emission found in UC HII regions in Sagittarius B2, yet they are smaller by an order of magnitude than the emission found in massive star clusters such as NGC 3603. Three possibilities are discussed for the cause of the hard extended emission in the Welch ring: an ensemble of unresolved point sources, shocked interacting winds of the young O stars, and a wind-blown bubble interacting with ambient cold matter.

astro-ph↗

arXiv2006

A Chandra/ACIS Study of 30 Doradus II. X-ray Point Sources in the Massive Star Cluster R136 and Beyond

We have studied the X-ray point source population of the 30 Doradus star-forming complex in the Large Magellanic Cloud using high-spatial-resolution X-ray images and spatially-resolved spectra obtained with the Advanced CCD Imaging Spectrometer (ACIS) aboard the Chandra X-ray Observatory. Here we describe the X-ray sources in a 17' x 17' field centered on R136, the massive star cluster at the center of the main 30 Dor nebula. We detect 20 of the 32 Wolf-Rayet stars in the ACIS field. R136 is resolved at the subarcsecond level into almost 100 X-ray sources, including many typical O3--O5 stars as well as a few bright X-ray sources previously reported. Over two orders of magnitude of scatter in L_X is seen among R136 O stars, suggesting that X-ray emission in the most massive stars depends critically on the details of wind properties and binarity of each system, rather than reflecting the widely-reported characteristic value L_X/L_bol ~ 10^{-7}. Such a canonical ratio may exist for single massive stars in R136, but our data are too shallow to confirm this relationship. Through this and future X-ray studies of 30 Doradus, the complete life cycle of a massive stellar cluster can be revealed.

astro-ph↗

arXiv2005

Membership of the Orion Nebula Population from the Chandra Orion Ultradeep Project

The Chandra Orion Ultradeep project (COUP) observation described in a companion paper by Getman et al. provides an exceptionally deep X-ray survey of the Orion Nebula Cluster and associated embedded young stellar objects. Membership of the region is important for studies of the stellar IMF, cluster dynamics, and star formation. The COUP study detected 1616 X-ray sources. In this study we confirm cloud membership for 1315 stars, identify 16 probable foreground field stars having optical counterparts with discrepant proper motions, and classify the remaining 285 X-ray sources, of which 51 are lightly and 234 heavily obscured. The 51 lightly obscured sources without known counterparts fall into three groups. (i) Sixteen are likely new members of the Orion Nebula Cluster. (ii) Two with unusually soft and non-flaring X-ray emission appear to be associated with nebular shocks, and may be new examples of X-rays produced at the bow shocks of Herbig-Haro outflows. (iii) The remaining thirty three are very weak uncertain sources, possibly spurious. Out of 234 heavily absorbed sources without optical or near-infrared counterparts 75 COUP sources are likely new embedded cloud members (with membership for 42 confirmed by powerful X-ray flares), and the remaining 159 are likely extragalactic AGN seen through the molecular cloud, as argued by a careful simulation of the extragalactic background population. Finally, a few new binary companions to Orion stars may have been found, but most cases of proximate COUP sources can be attributed to chance superpositions in this crowded field.

astro-ph↗

arXiv2005

COUP census of X-ray stars in BN-KL and OMC-1S

We present a study of the X-ray sources detected in the vicinity of two density peaks in the Orion Molecular Cloud 1 (OMC-1) behind the Orion Nebula Cluster (ONC), as seen in the exceptionally deep (~10 days) exposure of the Chandra Orion Ultradeep Project (COUP). We focus on a 40"*50" region around the Becklin-Neugebauer object and Kleinmann-Low nebula (collectively BN-KL) and a 60"*75" region around OMC-1S, a secondary star-forming peak some 90" south of BN-KL. Forty-three and sixty X-ray sources were detected in BN-KL and OMC-1S, respectively, of which half and one-third, respectively, were found to be foreground members of the ONC, while the remaining sources are identified as obscured X-ray sources with column densities 22<log(NH)/cm^{-2})<24. All but 5 and 18 of these sources have near-infrared stellar counterparts, and 22 of these appear to be young stellar objects (YSOs). X-ray sources are found close to four luminous mid-IR sources namely BN, IRc3-i2, IRc2-C, and Source n; their X-ray variability and spectral properties are typical of coronal activity in low-mass stars rather than wind emission from massive stars, suggesting that the X-ray emission may be arising from companions. The X-ray light curve of the X-ray source close to BN shows a periodicity of ~8.3 days and from an X-ray image deconvolution of the region around BN, we conclude that either BN itself or a low mass companion with a projected separation of ~200 AU was detected. On the other hand, no emission is seen from the bright radio Source I, held by some to be the main source of luminosity in BN-KL. In OMC-1S, Chandra unveils a new subcluster of seven YSOs without infrared counterparts (abridged).

astro-ph↗

arXiv2004

Chandra Orion Ultradeep Project: Observations and Source Lists

We present a description of the data reduction methods and the derived catalog of more than 1600 X-ray point sources from the exceptionally deep January 2003 Chandra X-ray Observatory observation of the Orion Nebula Cluster and embedded populations around OMC-1. The observation was obtained with Chandra's Advanced CCD Imaging Spectrometer (ACIS) and has been nicknamed the Chandra Orion Ultradeep Project (COUP). With an 838 ks exposure made over a continuous period of 13.2 days, the COUP observation provides the most uniform and comprehensive dataset on the X-ray emission of normal stars ever obtained in the history of X-ray astronomy.

astro-ph↗