arXiv subjects

James C. Green

Publications and source records attributed to James C. Green.

At least 19 recordsLinked to original sources

arXiv2023

Aberration corrected ultraviolet echelle spectrographs: straw man designs and performance

The Far Ultraviolet (FUV: hereafter 900-1150 A) is a spectral range which contains many of the ground state transitions of common elements but has had limited observational capabilities due to the unique technological requirements to operate in this waveband. Conceptual designs are presented, for high resolution (R > 50,000) echelle spectrographs for CubeSat, SMEX and MIDEX missions, along with comparisons of their performance to past instruments.

astro-ph.IM↗

arXiv2018

A Galaxy Redshift Survey near HST/COS AGN Sight Lines

To establish the connection between galaxies and UV-detected absorption systems in the local universe, a deep ($g\leq20$) and wide ($\sim20^{\prime}$ radius) galaxy redshift survey is presented around 47 sight lines to UV-bright AGN observed by the Cosmic Origins Spectrograph (COS). Specific COS science team papers have used this survey to connect absorbers to galaxies, groups of galaxies, and large-scale structures, including voids. Here we present the technical details of the survey and the basic measurements required for its use, including redshifts for individual galaxies and uncertainties determined collectively by spectral class (emission-line, absorption-line, and composite spectra) and completeness for each sight line as a function of impact parameter and magnitude. For most of these sight lines the design criteria of $>90$% completeness over a $>1$ Mpc region down to $\lesssim0.1\,L^*$ luminosities at $z\leq0.1$ allows a plausible association between low-$z$ absorbers and individual galaxies. Ly$α$ covering fractions are computed to approximate the star-forming and passive galaxy populations using the spectral classes above. In agreement with previous results, the covering fraction of star-forming galaxies with $L\geq0.3\,L^*$ is consistent with unity inside one virial radius and declines slowly to $>50$% at 4 virial radii. On the other hand, passive galaxies have lower covering fractions ($\sim60$%) and a shallower decline with impact parameter, suggesting that their gaseous halos are patchy but have a larger scale-length than star-forming galaxies. All spectra obtained by this project are made available electronically for individual measurement and use.

astro-ph.GA↗

arXiv2017

Characterizing the Circumgalactic Medium of Nearby Galaxies with HST/COS and HST/STIS Absorption-Line Spectroscopy: II. Methods and Models

We present basic data and modeling for a survey of the cool, photo-ionized Circum-Galactic Medium (CGM) of low-redshift galaxies using far-UV QSO absorption line probes. This survey consists of "targeted" and "serendipitous" CGM subsamples, originally described in Stocke et al. (2013, Paper 1). The targeted subsample probes low-luminosity, late-type galaxies at $z<0.02$ with small impact parameters ($\langleρ\rangle = 71$ kpc), and the serendipitous subsample probes higher luminosity galaxies at $z\lesssim0.2$ with larger impact parameters ($\langleρ\rangle = 222$ kpc). HST and FUSE UV spectroscopy of the absorbers and basic data for the associated galaxies, derived from ground-based imaging and spectroscopy, are presented. We find broad agreement with the COS-Halos results, but our sample shows no evidence for changing ionization parameter or hydrogen density with distance from the CGM host galaxy, probably because the COS-Halos survey probes the CGM at smaller impact parameters. We find at least two passive galaxies with H I and metal-line absorption, confirming the intriguing COS-Halos result that galaxies sometimes have cool gas halos despite no on-going star formation. Using a new methodology for fitting H I absorption complexes, we confirm the CGM cool gas mass of Paper 1, but this value is significantly smaller than found by the COS-Halos survey. We trace much of this difference to the specific values of the low-$z$ meta-galactic ionization rate assumed. After accounting for this difference, a best-value for the CGM cool gas mass is found by combining the results of both surveys to obtain $\log{(M/M_{\odot})}=10.5\pm0.3$, or ~30% of the total baryon reservoir of an $L \geq L^*$, star-forming galaxy.

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arXiv2015

An HST/COS Survey of the Low-Redshift IGM. I. Survey, Methodology, & Overall Results

We use high-quality, medium-resolution {\it Hubble Space Telescope}/Cosmic Origins Spectrograph (\HST/COS) observations of 82 UV-bright AGN at redshifts $z_{AGN}<0.85$ to construct the largest survey of the low-redshift intergalactic medium (IGM) to date: 5343 individual extragalactic absorption lines in HI and 25 different metal-ion species grouped into 2610 distinct redshift systems at $z_{abs}<0.75$ covering total redshift pathlengths $Δz_{HI}=21.7$ and $Δz_{OVI}=14.5$. Our semi-automated line-finding and measurement technique renders the catalog as objectively-defined as possible. The cumulative column-density distribution of HI systems can be parametrized $dN(>N)/dz=C_{14}(N/10^{14} cm^{-2})^{-(β-1)}$, with $C_{14}=25\pm1$ and $β=1.65\pm0.02$. This distribution is seen to evolve both in amplitude, $C_{14}\sim(1+z)^{2.0\pm0.1}$, and slope $β(z)=1.73-0.26 z$ for $z<0.47$. We observe metal lines in 427 systems, and find that the fraction of IGM absorbers detected in metals is strongly dependent on N_{HI}. The distribution of OVI absorbers appear to evolve in the same sense as the Lya forest. We calculate contributions to $Ω_b$ from different components of the low-$z$ IGM and determine the Lya decrement as a function of redshift. IGM absorbers are analyzed via a two-point correlation function (TPCF) in velocity space. We find substantial clustering of \HI\ absorbers on scales of $Δv=50-300$ km/s with no significant clustering at $Δv>1000$ km/s. Splitting the sample into strong and weak absorbers, we see that most of the clustering occurs in strong, $N_{HI}>10^{13.5} cm^{-2}$, metal-bearing IGM systems. The full catalog of absorption lines and fully-reduced spectra is available via MAST as a high-level science product at http://archive.stsci.edu/prepds/igm/.

astro-ph.CO↗

arXiv2015

The SLICE, CHESS, and SISTINE Ultraviolet Spectrographs: Rocket-borne Instrumentation Supporting Future Astrophysics Missions

NASA's suborbital program provides an opportunity to conduct unique science experiments above Earth's atmosphere and is a pipeline for the technology and personnel essential to future space astrophysics, heliophysics, and atmospheric science missions. In this paper, we describe three astronomy payloads developed (or in development) by the Ultraviolet Rocket Group at the University of Colorado. These far-ultraviolet (100 - 160 nm) spectrographic instruments are used to study a range of scientific topics, from gas in the interstellar medium (accessing diagnostics of material spanning five orders of magnitude in temperature in a single observation) to the energetic radiation environment of nearby exoplanetary systems. The three instruments, SLICE, CHESS, and SISTINE form a progression of instrument designs and component-level technology maturation. SLICE is a pathfinder instrument for the development of new data handling, storage, and telemetry techniques. CHESS and SISTINE are testbeds for technology and instrument design enabling high-resolution (R > 100,000) point source spectroscopy and high throughput imaging spectroscopy, respectively, in support of future Explorer, Probe, and Flagship-class missions. The CHESS and SISTINE payloads support the development and flight testing of large-format photon-counting detectors and advanced optical coatings: NASA's top two technology priorities for enabling a future flagship observatory (e.g., the LUVOIR Surveyor concept) that offers factors of roughly 50 - 100 gain in ultraviolet spectroscopy capability over the Hubble Space Telescope. We present the design, component level laboratory characterization, and flight results for these instruments.

astro-ph.IM↗

arXiv2013

H2 Excitation Structure on the Sightlines to delta Scorpius and zeta Ophiucus - First Results from the Sub-orbital Local Interstellar Cloud Experiment

We present the first science results from the Sub-orbital Local Interstellar Cloud Experiment (SLICE): moderate resolution 1020-1070A spectroscopy of four sightlines through the local interstellar medium. High signal-to-noise (S/N) spectra of eta Uma, alpha Vir, delta Sco, and zeta Oph were obtained during a 21 April 2013 rocket flight. The SLICE observations constrain the density, molecular photoexcitation rates, and physical conditions present in the interstellar material towards delta Sco and zeta Oph. Our spectra indicate a factor of two lower total N(H2) than previously reported for delta Sco, which we attribute to higher S/N and better scattered light control in the new SLICE observations. We find N(H2) = 1.5 x 10^{19} cm^{-2} on the delta Sco sightline, with kinetic and excitation temperatures of 67 and 529 K, respectively, and a cloud density of n_{H} = 56 cm^{-3}. Our observations of the bulk of the molecular sightline toward zeta Oph are consistent with previous measurements (N(H2) ~ 3 x 10^{20} cm^{-2} at T_{01} = 66 K and T_{exc} = 350 K). However, we detect significantly more rotationally excited H2 towards zeta Oph than previously observed. We infer a cloud density in the rotationally excited component of n_{H} ~ 7600 cm^{-3} and suggest that the increased column densities of excited H2 are a result of the ongoing interaction between zeta Oph and its environment; also manifest as the prominent mid-IR bowshock observed by WISE and the presence of vibrationally-excited H2 molecules observed by HST.

astro-ph.GA↗

arXiv2013

HST/COS Spectra of Three QSOs That Probe The Circumgalactic Medium of a Single Spiral Galaxy: Evidence for Gas Recycling and Outflow

We have used the Cosmic Origins Spectrograph (COS) to obtain far-UV spectra of three closely-spaced QSO sight lines that probe the circumgalactic medium (CGM) of an edge-on spiral galaxy, ESO 157-49, at impact parameters of 74 and 93 kpc near its major axis and 172 kpc along its minor axis. H I Lyα absorption is detected at the galaxy redshift in the spectra of all three QSOs, and metal lines of Si III, Si IV, and C IV are detected along the two major-axis sight lines. Photoionization models of these clouds suggest metallicities close to the galaxy metallicity, cloud sizes of ~1 kpc, and gas masses of ~10^4 solar masses. Given the high covering factor of these clouds, ESO 157-49 could harbor ~2x10^9 solar masses of warm CGM gas. We detect no metals in the sight line that probes the galaxy along its minor axis, but gas at the galaxy metallicity would not have detectable metal absorption with ionization conditions similar to the major-axis clouds. The kinematics of the major-axis clouds favor these being portions of a "galactic fountain" of recycled gas, while two of the three minor-axis clouds are constrained geometrically to be outflowing gas. In addition, one of our QSO sight lines probes a second more distant spiral, ESO 157-50, along its major axis at an impact parameter of 88 kpc. Strong H I Lyα and C IV absorption only are detected in the QSO spectrum at the redshift of ESO 157-50.

astro-ph.CO↗

arXiv2012

Characterizing the Circumgalactic Medium of Nearby Galaxies with HST/COS and HST/STIS Absorption-Line Spectroscopy

The Circumgalactic Medium (CGM) of late-type galaxies is characterized using UV spectroscopy of 11 targeted QSO/galaxy pairs at z < 0.02 with the Hubble Space Telescope Cosmic Origins Spectrograph and ~60 serendipitous absorber/galaxy pairs at z < 0.2 with the Space Telescope Imaging Spectrograph. CGM warm cloud properties are derived, including volume filling factors of 3-5%, cloud sizes of 0.1-30 kpc, masses of 10-1e8 solar masses and metallicities of 0.1-1 times solar. Almost all warm CGM clouds within 0.5 virial radii are metal-bearing and many have velocities consistent with being bound, "galactic fountain" clouds. For galaxies with L > 0.1 L*, the total mass in these warm CGM clouds approaches 1e10 solar masses, ~10-15% of the total baryons in massive spirals and comparable to the baryons in their parent galaxy disks. This leaves >50% of massive spiral-galaxy baryons "missing". Dwarfs (<0.1 L*) have smaller area covering factors and warm CGM masses (<5% baryon fraction), suggesting that many of their warm clouds escape. Constant warm cloud internal pressures as a function of impact parameter ($P/k ~ 10 cm^{-3} K) support the inference that previous COS detections of broad, shallow O VI and Ly-alpha absorptions are of an extensive (~400-600 kpc), hot (T ~ 1e6 K) intra-cloud gas which is very massive (>1e11 solar masses). While the warm CGM clouds cannot account for all the "missing baryons" in spirals, the hot intra-group gas can, and could account for ~20% of the cosmic baryon census at z ~ 0 if this hot gas is ubiquitous among spiral groups.

astro-ph.CO↗

arXiv2012

From Protoplanetary Disks to Extrasolar Planets: Understanding the Life Cycle of Circumstellar Gas with Ultraviolet Spectroscopy

Few scientific discoveries have captured the public imagination like the explosion of exoplanetary science during the past two decades. This work has fundamentally changed our picture of Earth's place in the Universe and led NASA to make significant investments towards understanding the demographics of exoplanetary systems and the conditions that lead to their formation. The story of the formation and evolution of exoplanetary systems is essentially the story of the circumstellar gas and dust that are initially present in the protostellar environment; in order to understand the variety of planetary systems observed, we need to understand the life cycle of circumstellar gas from its initial conditions in protoplanetary disks to its endpoint as planets and their atmospheres. In this white paper response to NASA's Request for Information "Science Objectives and Requirements for the Next NASA UV/Visible Astrophysics Mission Concepts (NNH12ZDA008L)", we describe scientific programs that would use the unique capabilities of a future NASA ultraviolet (UV)/visible space observatory to make order-of-magnitude advances in our understanding of the life cycle of circumstellar gas.

astro-ph.SR↗

arXiv2012

On the Significance of Absorption Features in HST/COS Data

We present empirical scaling relations for the significance of absorption features detected in medium resolution, far-UV spectra obtained with the Cosmic Origins Spectrograph (COS). These relations properly account for both the extended wings of the COS line spread function and the non-Poissonian noise properties of the data, which we characterize for the first time, and predict limiting equivalent widths that deviate from the empirical behavior by \leq 5% when the wavelength and Doppler parameter are in the ranges λ= 1150-1750 A and b > 10 km/s. We have tested a number of coaddition algorithms and find the noise properties of individual exposures to be closer to the Poissonian ideal than coadded data in all cases. For unresolved absorption lines, limiting equivalent widths for coadded data are 6% larger than limiting equivalent widths derived from individual exposures with the same signal-to-noise. This ratio scales with b-value for resolved absorption lines, with coadded data having a limiting equivalent width that is 25% larger than individual exposures when b \approx 150 km/s.

astro-ph.IM↗

arXiv2012

Characterizing CO Fourth Positive Emission in Young Circumstellar Disks

Carbon Monoxide is a commonly used IR/sub-mm tracer of gas in protoplanetary disks. We present an analysis of ultraviolet CO emission in {HST}-COS spectra for 12 Classical T Tauri stars. Several ro-vibrational bands of the CO A^1Π- X^1Σ^+ (Fourth Positive) electronic transition system are spectrally resolved from emission of other atoms and H_2. The CO A^1Πv'=14 state is populated by absorption of Lyαphotons, created at the accretion column on the stellar surface. For targets with strong CO emission, we model the Lyαradiation field as an input for a simple fluorescence model to estimate CO rotational excitation temperatures and column densities. Typical column densities range from N_{CO} = 10^{18} - 10^{19} cm^{-2}. Our measured excitation temperatures are mostly below T_{CO} = 600 K, cooler than typical M-band CO emission. These temperatures and the emission line widths imply that the UV emission originates in a different population of CO than that which is IR-emitting. We also find a significant correlation between CO emission and the disk accretion rate M_{acc} and age. Our analysis shows that ultraviolet CO emission can be a useful diagnostic of CTTS disk gas.

astro-ph.EP↗

arXiv2011

The Cosmic Origins Spectrograph

The Cosmic Origins Spectrograph (COS) is a moderate-resolution spectrograph with unprecedented sensitivity that was installed into the Hubble Space Telescope (HST) in May 2009, during HST Servicing Mission 4 (STS-125). We present the design philosophy and summarize the key characteristics of the instrument that will be of interest to potential observers. For faint targets, with flux F_lambda ~ 1.0E10-14 ergs/s/cm2/Angstrom, COS can achieve comparable signal to noise (when compared to STIS echelle modes) in 1-2% of the observing time. This has led to a significant increase in the total data volume and data quality available to the community. For example, in the first 20 months of science operation (September 2009 - June 2011) the cumulative redshift pathlength of extragalactic sight lines sampled by COS is 9 times that sampled at moderate resolution in 19 previous years of Hubble observations. COS programs have observed 214 distinct lines of sight suitable for study of the intergalactic medium as of June 2011. COS has measured, for the first time with high reliability, broad Lya absorbers and Ne VIII in the intergalactic medium, and observed the HeII reionization epoch along multiple sightlines. COS has detected the first CO emission and absorption in the UV spectra of low-mass circumstellar disks at the epoch of giant planet formation, and detected multiple ionization states of metals in extra-solar planetary atmospheres. In the coming years, COS will continue its census of intergalactic gas, probe galactic and cosmic structure, and explore physics in our solar system and Galaxy.

astro-ph.IM↗

arXiv2011

An HST/COS Search for Warm-Hot Baryons in the Mrk421 Sightline

Thermally-broadened Lya absorbers (BLAs) offer an alternate method to using highly-ionized metal absorbers (OVI, OVII, etc.) to probe the warm-hot intergalactic medium (WHIM, T=10^5-10^7 K). Until now, WHIM surveys via BLAs have been no less ambiguous than those via far-UV and X-ray metal-ion probes. Detecting these weak, broad features requires background sources with a well-characterized far-UV continuum and data of very high quality. However, a recent HST/COS observation of the z=0.03 blazar Mrk421 allows us to perform a metal-independent search for WHIM gas with unprecedented precision. The data have high signal-to-noise (S/N~50 per ~20 km/s resolution element) and the smooth, power-law blazar spectrum allows a fully-parametric continuum model. We analyze the Mrk421 sight line for BLA absorbers, particularly for counterparts to the proposed OVII WHIM systems reported by Nicastro et al. (2005a,b) based on Chandra/LETG observations. We derive the Lya profiles predicted by the X-ray observations. The signal-to-noise ratio of the COS data is high (S/N~25 per pixel), but much higher S/N can be obtained by binning the data to widths characteristic of the expected BLA profiles. With this technique, we are sensitive to WHIM gas over a large (N_H, T) parameter range in the Mrk421 sight line. We rule out the claimed Nicastro et al. OVII detections at their nominal temperatures (T~1-2x10^6 K) and metallicities (Z=0.1 Z_sun) at >2 sigma level. However, WHIM gas at higher temperatures and/or higher metallicities is consistent with our COS non-detections.

astro-ph.CO↗

arXiv2011

The Far-Ultraviolet "Continuum" in Protoplanetary Disk Systems II: CO Fourth Positive Emission and Absorption

We exploit the high sensitivity and moderate spectral resolution of the $HST$-Cosmic Origins Spectrograph to detect far-ultraviolet spectral features of carbon monoxide (CO) present in the inner regions of protoplanetary disks for the first time. We present spectra of the classical T Tauri stars HN Tau, RECX-11, and V4046 Sgr, representative of a range of CO radiative processes. HN Tau shows CO bands in absorption against the accretion continuum. We measure a CO column density and rotational excitation temperature of N(CO) = 2 +/- 1 $\times$ 10$^{17}$ cm$^{-2}$ and T_rot(CO) 500 +/- 200 K for the absorbing gas. We also detect CO A-X band emission in RECX-11 and V4046 Sgr, excited by ultraviolet line photons, predominantly HI LyA. All three objects show emission from CO bands at $λ$ $>$ 1560 Å, which may be excited by a combination of UV photons and collisions with non-thermal electrons. In previous observations these emission processes were not accounted for due to blending with emission from the accretion shock, collisionally excited H$_{2}$, and photo-excited H2; all of which appeared as a "continuum" whose components could not be separated. The CO emission spectrum is strongly dependent upon the shape of the incident stellar LyA emission profile. We find CO parameters in the range: N(CO) 10$^{18-19}$ cm$^{-2}$, T_{rot}(CO) > 300 K for the LyA-pumped emission. We combine these results with recent work on photo- and collisionally-excited H$_{2}$ emission, concluding that the observations of ultraviolet-emitting CO and H2 are consistent with a common spatial origin. We suggest that the CO/H2 ratio in the inner disk is ~1, a transition between the much lower interstellar value and the higher value observed in solar system comets today, a result that will require future observational and theoretical study to confirm.

astro-ph.EP↗

arXiv2010

Diffuse Far-UV Line Emission from the Low-Redshift Lyman Break Galaxy Analog KISSR242

We present new ultraviolet (UV) observations of the luminous compact blue galaxy KISSR242, obtained with the HST-COS. We identify multiple resolved sub-arcsecond near-UV sources within the COS aperture. The far-UV spectroscopic data show strong outflow absorption lines, consistent with feedback processes related to an episode of massive star-formation. OI, CII, and SiII--SiIV are observed with a mean outflow velocity v_{out} = -60 km/s. We also detect faint fine-structure emission lines of singly ionized silicon for the first time in a low-redshift starburst galaxy. These emissions have been seen previously in deep Lyman break galaxy surveys at z ~ 3. The SiII* lines are at the galaxy rest velocity, and they exhibit a quantitatively different line profile from the absorption features. These lines have a width of ~ 75 km/s, too broad for point-like emission sources such as the HII regions surrounding individual star clusters. The size of the SiII* emitting region is estimated to be ~ 250 pc. We discuss the possibility of this emission arising in overlapping super star cluster HII regions, but find this explanation to be unlikely in light of existing far-UV observations of local star-forming galaxies. We suggest that the observed SiII* emission originates in a diffuse warm halo populated by interstellar gas driven out by intense star-formation and/or accreted during a recent interaction that may be fueling the present starburst episode in KISSR242.

astro-ph.CO↗

arXiv2010

Cosmic Origins Spectrograph Detection of Ne VIII Tracing Warm - Hot Gas Towards PKS 0405-123

We report on the detection of Ne VIII in the HST/Cosmic Origins Spectrograph spectrum of the intervening absorption system at z = 0.495096 towards PKS 0405-123. The high S/N COS spectrum also covers absorption from H I, C III, O III, O IV and O VI associated with this multiphase system. The Ne VIII is detected with high significance in both lines of the doublet, with integrated column densities of log Na(Ne VIII 770) = 13.96 +/- 0.06 dex and log Na(Ne VIII 780) = 14.08 +/- 0.07 dex. We find the origin of Ne VIII consistent with collisionally ionized gas at T ~ 5 x 10^5 K with a large baryonic column density of N(H) ~ 10^{19} - 10^{20} cm^-2. The metallicity in the Ne VIII gas phase is estimated to be [Ne/H] ~ -0.6 +/- 0.3 dex. The intermediate ions such as C III, O III, O IV and H I are consistent with photoionization in lower ionization gas at T ~ 10,000 K. The O V and O VI in this absorber can have contributions from both the photoionized and collisionally ionized gas phases. The absorber is at 180 km/s systematic velocity and 110 kpc projected separation from a M_R = -19.6 galaxy of extended morphology. The collisionally ionized gas at T ~ 5 x 10^5 K points to an origin in multiphase gas embedded in the hot halo of the galaxy, or in a nearby WHIM structure. The high sensitivity UV spectroscopy afforded by COS has opened up new opportunities for discovering large reservoirs of "missing baryons" in the low-z universe through the detection of Ne VIII systems.

astro-ph.CO↗

arXiv2010

Observations of Mass Loss from the Transiting Exoplanet HD 209458b

Using the new Cosmic Origins Spectrograph (COS) on the {\it Hubble Space Telescope (HST)}, we obtained moderate-resolution, high signal/noise ultraviolet spectra of HD 209458 and its exoplanet HD 209458b during transit, both orbital quadratures, and secondary eclipse. We compare transit spectra with spectra obtained at non-transit phases to identify spectral features due to the exoplanet's expanding atmosphere. We find that the mean flux decreased by $7.8\pm 1.3$% for the C II 1334.5323Å and 1335.6854Å lines and by $8.2\pm 1.4$% for the Si III 1206.500Å line during transit compared to non-transit times in the velocity interval --50 to +50 km s$^{-1}$. Comparison of the C II and Si III line depths and transit/non-transit line ratios shows deeper absorption features near --10 and +15 km s$^{-1}$ and less certain features near --40 and +30--70 km s$^{-1}$, but future observations are needed to verify this first detection of velocity structure in the expanding atmosphere of an exoplanet. Our results for the C II lines and the non-detection of Si IV 1394.76Å absorption are in agreement with \citet{Vidal-Madjar2004}, but we find absorption during transit in the Si III line contrary to the earlier result. The $8\pm 1$% obscuration of the star during transit is far larger than the 1.5% obscuration by the exoplanet's disk. Absorption during transit at velocities between --50 and +50 km s$^{-1}$ in the C II and Si III lines requires high-velocity ion absorbers, but models that assume that the absorbers are high-temperature thermal ions are inconsistent with the COS spectra. Assuming hydrodynamic model values for the gas temperature and outflow velocity at the limb of the outflow as seen in the C II lines, we find mass-loss rates in the range (8--40)$\times 10^{10}$ g s$^{-1}$.

astro-ph.EP↗

arXiv2010

Searching for Far-Ultraviolet Auroral/Dayglow Emission from HD209458b

We present recent observations from the HST-Cosmic Origins Spectrograph aimed at characterizing the auroral emission from the extrasolar planet HD209458b. We obtained medium-resolution (R~18-20,000) far-ultraviolet (1150-1700A) spectra at both the Phase 0.25 and Phase 0.75 quadrature positions as well as a stellar baseline measurement at secondary eclipse. This analysis includes a catalog of stellar emission lines and a star-subtracted spectrum of the planet. We present an emission model for planetary H2 emission, and compare this model to the planetary spectrum. No unambiguously identifiable atomic or molecular features are detected, and upper limits are presented for auroral/dayglow line strengths. An orbital velocity cross-correlation analysis finds a statistically significant (3.8 sigma) feature at +15 (+/- 20) km/s in the rest frame of the planet, at 1582 A. This feature is consistent with emission from H2 B-X (2-9) P(4) (lambda_{rest} = 1581.11 A), however the physical mechanism required to excite this transition is unclear. We compare limits on relative line strengths seen in the exoplanet spectrum with models of ultraviolet fluorescence to constrain the atmospheric column density of neutral hydrogen between the star and the planetary surface. These results support models of short period extrasolar giant planets with weak magnetic fields and extended atomic atmospheres.

astro-ph.EP↗