FUV Data Research Articles

Evaluating Auroral Forecasts Against Satellite Observations Under Different Levels of Geomagnetic Activity

AbstractThe aurora and associated high energy particles and currents pose a space weather hazard to communication networks and ground‐based infrastructure. Forecasting the location of the auroral oval forms an integral component of daily space weather operations. We evaluate a version of the OVATION‐Prime 2013 auroral forecast model that was implemented for operational use at the UK Met Office Space Weather Operations Cent. Building on our earlier studies, we evaluate the ability of the OVATION‐Prime 2013 model to predict the location of the auroral oval in all latitude and local time sectors under different levels of geomagnetic activity, defined by Kp. We compare the model predictions against auroral boundaries determined from IMAGE FUV data. Our analysis shows that the model performs well at predicting the equatorward extent of the auroral oval, particularly as the equatorward auroral boundary expands to lower latitudes for increasing Kp levels. The model performance is reduced in the high latitude region near the poleward auroral boundary, particularly in the nightside sectors where the model does not accurately capture the expansion and contraction of the polar cap as the open flux content of the magnetosphere changes. For increasing levels of geomagnetic activity (Kp ≥ 3), the performance of the model decreases, with the poleward edge of the auroral oval typically observed at lower latitudes than forecast. As such, the forecast poleward edge of the auroral oval is less reliable during more active and hazardous intervals.

An AstroSat/UVIT study of galaxies in the cluster Abell 2199

We present the newly acquired data for an AstroSat/UVIT field centred on a face-on spiral starburst galaxy UGC 10420, located in the X-ray bright cluster Abell 2199 (z = 0.031). We have analysed the FUV BaF2 data for this field along with the archival FUV and NUV data from the GALEX mission, optical photometric data from the SDSS, spectroscopic data from the literature, and low-frequency radio data from the LoTSS survey, respectively. The stars were separated from the galaxies using the SDSS photometric pipeline classification, while the spectroscopic redshifts available for 35% of the detected UVIT sources were used to identify member galaxies of the cluster Abell 2199. We find that (a) the non-cluster galaxies are on average fainter than the cluster galaxies at fixed magnitude, (b) stars and galaxies are indistinguishable in the r vs. NUV–r plane, and (c) bright stars are ∼ 1.5 mag bluer than the galaxies in the FUV–r vs. NUV–r colour-colour plane. Besides UGC 10420 which is the only known cluster galaxy with an extended-UV disk, we identify five more galaxies with asymmetric FUV morphology and extended radio emission in this field. All the asymmetric member galaxies of Abell 2199, lie within the virial boundaries of the cluster. This observation, together with the fact that these asymmetric cluster galaxies have low-frequency radio tails or FUV emission pointing away from the cluster centre leads us to hypothesise that these galaxies are likely undergoing ram-pressure stripping (RPS) under the influence of cluster-environment related mechanisms. A comparison of optical and FUV star formation rate of UVIT detected galaxies shows enhanced star formation in half of the RPS candidates, suggesting that environment-related mechanisms may lead to a burst of star formation in RPS galaxies.Our analysis indicates the presence of at least two more groups or clusters at z ∼ 0.077 and 0.260, coincident with Abell 2199 along the line of sight of the field of view studied here.

A GALEX view of the DA white dwarf population

ABSTRACT We present a detailed model atmosphere analysis of 14001 DA white dwarfs from the Montreal White Dwarf Database with ultraviolet photometry from the GALEX mission. We use the 100 pc sample, where the extinction is negligible, to demonstrate that there are no major systematic differences between the best-fitting parameters derived from optical only data and the optical + UV photometry. GALEX FUV and NUV data improve the statistical errors in the model fits, especially for the hotter white dwarfs with spectral energy distributions that peak in the UV. Fitting the UV to optical spectral energy distributions also reveals UV-excess or UV-deficit objects. We use two different methods to identify outliers in our model fits. Known outliers include objects with unusual atmospheric compositions, strongly magnetic white dwarfs, and binary white dwarfs, including double degenerates and white dwarf + main-sequence systems. We present a list of 89 newly identified outliers based on GALEX UV data; follow-up observations of these objects will be required to constrain their nature. Several current and upcoming large-scale spectroscopic surveys are targeting >105 white dwarfs. In addition, the ULTRASAT mission is planning an all-sky survey in the NUV band. A combination of the UV data from GALEX and ULTRASAT and optical data on these large samples of spectroscopically confirmed DA white dwarfs will provide an excellent opportunity to identify unusual white dwarfs in the solar neighbourhood.

WALLABY Pilot Survey: hydra cluster galaxies UV and H imorphometrics

ABSTRACTGalaxy morphology in atomic hydrogen (H i) and in the ultraviolet (UV) are closely linked. This has motivated their combined use to quantify morphology over the full H i disc for both H i and UV imaging. We apply galaxy morphometrics: concentration, asymmetry, gini, M20 and multimode-intensity-deviation statistics to the first moment-0 maps of the WALLABY Survey of galaxies in the hydra cluster centre. Taking advantage of this new H i survey, we apply the same morphometrics over the full H i extent on archival GALEX FUV and NUV data to explore how well H i truncated, extended ultraviolet disc (XUV) and other morphological phenomena can be captured using pipeline WALLABY data products. Extended H i and UV discs can be identified relatively straightforward from their respective concentration. Combined with WALLABY H i, even the shallowest GALEX data are sufficient to identify XUV discs. Our second goal is to isolate galaxies undergoing ram-pressure stripping in the H i morphometric space. We employ four different machine learning techniques, a decision tree, a k-nearest neighbour, a support-vector machine, and a random forest. Up to 80 per cent precision and recall are possible with the random forest giving the most robust results.

Galaxy And Mass Assembly (GAMA): Defining passive galaxy samples and searching for the UV upturn

ABSTRACT We use data from the GAMA and GALEX surveys to demonstrate that the UV upturn, an unexpected excess of ultraviolet flux from a hot stellar component, seen in the spectra of many early-type galaxies, arises from processes internal to individual galaxies with no measurable influence from the galaxies’ larger environment. We first define a clean sample of passive galaxies without a significant contribution to their UV flux from low-level star formation. We confirm that galaxies with the optical colours of red sequence galaxies often have signs of residual star formation, which, without other information, would prevent a convincing demonstration of the presence of UV upturns. However, by including (NUV−u) and WISE (W2–W3) colours, and FUV data where it exists, we can convincingly constrain samples to be composed of non-star-forming objects. Using such a sample, we examine GALEX photometry of low-redshift GAMA galaxies in a range of low-density environments, from groups to the general field, searching for UV upturns. We find a wide range of (NUV−r) colours, entirely consistent with the range seen – and attributed to the UV upturn – in low-redshift red sequence cluster galaxies. The range of colours is independent of group multiplicity or velocity dispersion, with isolated passive galaxies just as likely to have blue UV-to-optical colours, implying significant upturn components, as those in richer groups and in the previous data on clusters. This is supported by equivalent results for (FUV−r) colours which are clear indicators of upturn components.

Observational Signature of Circumstellar Interaction and 56Ni-mixing in the Type II Supernova 2016gfy

Abstract The optical and ultraviolet broadband photometric and spectroscopic observations of the Type II supernova (SN) 2016gfy are presented. The V-band light curve (LC) shows a distinct plateau phase with a slope of s 2 ∼ 0.12 mag (100 day)−1 and a duration of 90 ± 5 days. Detailed analysis of SN 2016gfy provided a mean 56Ni mass of 0.033 ± 0.003 M ⊙, a progenitor radius of ∼350–700 R ⊙, a progenitor mass of ∼12–15 M ⊙, and an explosion energy of (0.9–1.4) × 1051 erg s−1. The P-Cygni profile of Hα in the early-phase spectra (∼11–21 days) shows a boxy emission. Assuming that this profile arises from the interaction of the SN ejecta with the pre-existing circumstellar material (CSM), it is inferred that the progenitor underwent a recent episode (30–80 yr prior to the explosion) of enhanced mass loss. Numerical modeling suggests that the early LC peak is reproduced better with an existing CSM of 0.15 M ⊙ spread out to ∼70 au. A late-plateau bump is seen in the VRI LCs during ∼50–95 days. This bump is explained as a result of the CSM interaction and/or partial mixing of radioactive 56Ni in the SN ejecta. Using strong-line diagnostics, a subsolar oxygen abundance is estimated for the supernova H ii region (12 + log(O/H) = 8.50 ± 0.11), indicating an average metallicity for the host of an SN II. A star formation rate of ∼8.5 M ⊙ yr−1 is estimated for NGC 2276 using the archival GALEX FUV data.

The First Ultraviolet Detection of the Large Magellanic Cloud Pulsar PSR B0540–69 and Its Multi-wavelength Properties

Abstract We observed the young (∼1700 yr) pulsar PSR B0540−69 in the ultraviolet for the first time with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. Imaging observations with the NUV-MAMA and ultraviolet FUV-MAMA detectors in TIME-TAG mode allowed us to clearly detect the pulsar in two bands around 2350 and 1590 Å, with magnitudes m NUV = 21.45 ± 0.02 and m FUV = 21.83 ± 0.10. We also detected the pulsar wind nebula in the NUV-MAMA image, with a morphology similar to that observed in the optical and near-infrared (IR). The extinction-corrected NUV and FUV pulsar fluxes are compatible with a very steep power-law spectrum with spectral index α UV ∼ 3, and incompatible with a Rayleigh–Jeans spectrum, indicating a non-thermal origin of the emission. The comparison with the optical/near-IR power-law spectrum (spectral index α O,nIR ∼ 0.7), indicates an abrupt turnover at wavelengths below 2500 Å, not yet observed in other pulsars. We detected pulsations in both the NUV and FUV data at the 50 ms pulsar period. In both cases, the folded light curve features a broad pulse with two peaks closely spaced in phase, as observed in the optical and X-ray light curves. The NUV/FUV peaks are also aligned in phase with those observed in the radio (1.4 GHz), optical, X-ray, and γ-ray light curves, as in the Crab pulsar, implying a similar beaming geometry across all wavelengths. PSR B0540−69 is now the fifth isolated pulsar, together with Crab, Vela, PSR B0656+14, and the radio-quiet Geminga, detected in the optical, UV, near-IR, X-rays, and γ-rays, and seen to pulsate in at least four of these energy bands.

Simultaneous spectroscopic and photometric analysis of galaxies with starlight: CALIFA+GALEX

We present an extended version of the spectral synthesis code STARLIGHT designed to incorporate both $\lambda$-by-$\lambda$ spectra and photometric fluxes in the estimation of stellar population properties of galaxies. The code is tested with simulations and data for 260 galaxies culled from the CALIFA survey, spatially matching the 3700--7000 \AA\ optical datacubes to GALEX near and far UV images. The sample spans E--Sd galaxies with masses from $10^9$ to $10^{12} M_\odot$ and stellar populations all the way from star-forming to old, passive systems. Comparing results derived from purely optical fits with those which also consider the NUV and FUV data we find that: (1) The new code is capable of matching the input UV data within the errors while keeping the quality of the optical fit essentially unchanged. (2) Despite being unreliable predictors of the UV fluxes, purely optical fits yield stellar population properties which agree well with those obtained in optical+UV fits for nearly 90% of our sample. (3) The addition of UV constraints has little impact on properties such as stellar mass and dust optical depth. Mean stellar ages and metallicities also remain nearly the same for most galaxies, the exception being low-mass, late-type galaxies, which become older and less enriched due to rearrangements of their youngest populations. (4) The revised ages are better correlated with observables such as the 4000 \AA\ break index, and the $NUV - r$ and $u - r$ colours, an empirical indication that the addition of UV constraints helps mitigating the effects of age-metallicity-extinction degeneracies.

Far-ultraviolet morphology of star-forming filaments in cool core brightest cluster galaxies

We present a multiwavelength morphological analysis of star-forming clouds and filaments in the central (≲50 kpc) regions of 16 low-redshift (z < 0.3) cool core brightest cluster galaxies. New Hubble Space Telescope imaging of far-ultraviolet continuum emission from young (≲10 Myr), massive (≳5 M⊙) stars reveals filamentary and clumpy morphologies, which we quantify by means of structural indices. The FUV data are compared with X-ray, Lyα, narrow-band Hα, broad-band optical/IR, and radio maps, providing a high spatial resolution atlas of star formation locales relative to the ambient hot (∼107–8 K) and warm ionized (∼104 K) gas phases, as well as the old stellar population and radio-bright active galactic nucleus (AGN) outflows. Nearly half of the sample possesses kpc-scale filaments that, in projection, extend towards and around radio lobes and/or X-ray cavities. These filaments may have been uplifted by the propagating jet or buoyant X-ray bubble, or may have formed in situ by cloud collapse at the interface of a radio lobe or rapid cooling in a cavity's compressed shell. The morphological diversity of nearly the entire FUV sample is reproduced by recent hydrodynamical simulations in which the AGN powers a self-regulating rain of thermally unstable star-forming clouds that precipitate from the hot atmosphere. In this model, precipitation triggers where the cooling-to-free-fall time ratio is tcool/tff ∼ 10. This condition is roughly met at the maximal projected FUV radius for more than half of our sample, and clustering about this ratio is stronger for sources with higher star formation rates.

HST far-ultraviolet imaging of DG Tauri

One of the best-studied jets from all young stellar objects is the jet of DG Tau, which we imaged in the FUV with HST for the first time. These high spatial resolution images were obtained with long-pass filters and allow us to construct images tracing mainly molecular hydrogen and C IV emission. We find that the H2 emission appears as a limb-brightened cone with additional emission close to the jet axis. The length of the rims is about 0.3 arcsec or 42 AU (proj.) before their brightness strongly drops, and the opening angle is about 90 deg. Comparing our FUV data with near-IR data we find that the fluorescent H2 emission likely traces the outer, cooler part of the disk wind while an origin of the H2 emission in the surface layers (atmosphere) of the (flared) disk is unlikely. Furthermore, the spatial shape of the H2 emission shows little variation over six years which suggests that the outer part of the disk wind is rather stable and probably not associated with the formation of individual knots. The C IV image shows that the emission is concentrated towards the jet axis. We find no indications for additional C IV emission at larger distances, which strengthens the association with the X-ray emission observed to originate within the DG Tau jet.

A comparison between star formation rate diagnostics and rate of core collapse supernovae within 11 Mpc

The core collapse supernova (CCSN) rate provides a strong lower limit for the star formation rate (SFR). Progress in using it as a cosmic SFR tracer requires some confidence that it is consistent with more conventional SFR diagnostics in the nearby Universe. This paper compares standard SFR measurements based on Halpha, FUV and TIR galaxy luminosities with the observed CCSN rate in the same galaxy sample. The comparison can be viewed from two perspectives. Firstly, by adopting an estimate of the minimum stellar mass to produce a CCSN one can determine a SFR from SN numbers. Secondly, the radiative SFRs can be assumed to be robust and then the SN statistics provide a constrain on the minimum stellar mass for CCSN progenitors. The novel aspect of this study is that Halpha, FUV and TIR luminosities are now available for a complete galaxy sample within the local 11Mpc volume and the number of discovered SNe in this sample within the last 13 years is high enough to perform a meaningful statistical comparison. We exploit the multi-wavelength dataset from 11HUGS, a volume-limited survey designed to provide a census of SFR in the local Volume. Assuming a lower limit for CCSN progenitors of 8 Msun, the CCSN rate matches the SFR from the FUV luminosity. However the SFR based on Halpha luminosity is lower than these two estimates by a factor of nearly 2. If we assume that the FUV or Halpha based luminosities are a true reflection of the SFR, we find that the minimum mass for CCSN progenitors is 8 +/- 1 Msun, and 6 +/- 1 Msun, respectively. The estimate of the minimum mass for CCSN progenitors obtained exploiting FUV data is in good agreement with that from the direct detection of CCSN progenitors. The concordant results by these independent methods point toward a constraint of 8 +/- 1 Msun on the lower mass limit for progenitor stars of CCSNe.

The reliability of [C ii] as an indicator of the star formation rate

The [CII] 157.74 \mu m line is an important coolant for the neutral interstellar gas. Since [CII] is the brightest spectral line for most galaxies, it is a potentially powerful tracer of star formation activity. In this paper we present a calibration of the star formation rate as a function of the [CII] luminosity for a sample of 24 star-forming galaxies in the nearby universe. This sample includes objects classified as HII regions or LINERs, but omits all Seyfert galaxies with a significant AGN contribution to the mid-infrared photometry. In order to calibrate the SFR against the line luminosity, we rely on both GALEX FUV data, which is an ideal tracer of the unobscured star formation, and MIPS 24 \mu m, to probe the dust-enshrouded fraction of star formation. In case of normal star-forming galaxies, the [CII] luminosity correlates well with the star formation rate. However, the extension of this relation to more quiescent (Halpha EW <= 10 A) or ultraluminous galaxies should be handled with caution, since these objects show a non-linearity in the L([CII])-to-L(FIR) ratio as a function of L(FIR) (and thus, their star formation activity). We provide two possible explanations for the origin of the tight correlation between the [CII] emission and the star formation activity on a global galaxy-scale. A first interpretation could be that the [CII] emission from PDRs arises from the immediate surroundings of star-forming regions. Since PDRs are neutral regions of warm dense gas at the boundaries between HII regions and molecular clouds and they provide the bulk of [CII] emission in most galaxies, we believe that a more or less constant contribution from these outer layers of photon-dominated molecular clumps to the [CII] emission provides a straightforward explanation for this close link between the [CII] luminosity and SFR. Alternatively,... (abridged)

THE SUPER-LINEAR SLOPE OF THE SPATIALLY RESOLVED STAR FORMATION LAW IN NGC 3521 AND NGC 5194 (M51a)

We have conducted interferometric observations with CARMA and an OTF mapping with the 45-m telescope at NRO in the CO (J=1-0) emission line of NGC 3521. Combining these new data, together with CARMA+NRO45 data for M51a and archival SINGS H$\alpha$, 24$\mu$m, THINGS H I and GALEX FUV data for both galaxies, we investigate the empirical scaling law that connects the surface density of SFR and cold gas (the Schmidt-Kennicutt law) on a spatially-resolved basis. We argue that plausibly deriving SFR maps of nearby galaxies requires the diffuse stellar/dust background emission to be carefully subtracted. An approach to complete this task is presented and applied in our pixel-by-pixel analysis on both galaxies, showing that the controversial results whether the molecular S-K law is super-linear or basically linear is a result of removing or preserving the local background. In both galaxies, the power index of the molecular S-K law is 1.5-1.9 at the highest available resolution (230 pc), and decreases monotonically for decreasing resolution; while the scatter (mainly intrinsic) increases as the resolution becomes higher, indicating a trend for which the S-K law breaks down below some scale. Both quantities are systematically larger in M51a than in NGC 3521, but when plotted against the de-projected scale (\delta_{dp}), they become highly consistent between the two galaxies, tentatively suggesting that the sub-kpc molecular S-K law in spiral galaxies depends only on the considered scale, without varying amongst spiral galaxies. A logarithmic function \gamma_{H_2}=-1.1 log[\delta_{dp}/kpc]+1.4 and a linear relation \sigma_{H_2}=-0.2 [\delta_{dp}/kpc]+0.7 are obtained through fitting to the M51a data, which describes both galaxies impressively well on sub-kpc scales. A larger sample of galaxies with better quality data are required to test the general applicability of these relations.

TAKING ADVANTAGE OF THE COS TIME-TAG CAPABILITY: OBSERVATIONS OF PULSATING HOT DQ WHITE DWARFS AND DISCOVERY OF A NEW ONE

We present an analysis of the ultraviolet light curves of five Hot DQ white dwarfs recently observed with the Cosmic Origins Spectrograph (COS) on board the Hubble Space Telescope (HST). These light curves were constructed by extracting the time-tag information from the FUV and NUV spectroscopic data. Single-color light curves were thus produced in 60 s time bins. The Fourier analysis of these data successfully recovers the main pulsation modes of the three stars previously known to be variable from ground-based observations. We also report the discovery of pulsations in another object, SDSS J1153+0056, making it only the fifth member of the new class of variable Hot DQ stars and the first pulsating white dwarf to be discovered from space-based observations. The relatively high amplitudes of the modes observed in the FUV (2–4 times that observed in the optical) as well as the high fraction of stars variable in our sample suggest that most, if not all, Hot DQ white dwarfs might be pulsating at some level when observed at high enough sensitivity. Our results also underline the vast potential of the time-tag capability of the HST/COS combination.

The Reliability of [C II] as a Star Formation Rate Indicator

AbstractWe present a calibration of the star formation rate (SFR) as a function of the [C II] 157.74 μm luminosity for a sample of 24 star-forming galaxies in the nearby universe. In order to calibrate the SFR against the line luminosity, we rely on both GALEX FUV data, which is an ideal tracer of the unobscured star formation, and Spitzer MIPS 24 μm, to probe the dust-enshrouded fraction of star formation. For this sample of normal star-forming galaxies, the [C II] luminosity correlates well with the star formation rate. However, the extension of this relation to more quiescent (Hα EW≤10 Å) or ultra luminous galaxies (L

NGC 4262: a Virgo galaxy with an extended ultraviolet ring

Context. The Galaxy Ultraviolet Explorer (GALEX) satellite has recently shown the presence of an extended, outer ring studded with UV-bright knots surrounding the lenticular galaxy NGC 4262. Such a structure-not detected in the optical-is coupled with a ring of atomic (HI) gas.Aims. We want to show that both star-forming and HI rings surrounding this SB0 galaxy share the same radial distance from the galaxy center and spatial orientation. We also model the kinematics of the ring(s) and of the galaxy body.Methods. We make use of archive FUV and NUV GALEX data plus HI observations from the literature.Results. We confirm that the UV-bright and atomic gas rings of NGC 4262 have the same extent and projected spatial orientation. Their kinematics is not coupled with that of the galaxy stars.Conclusions. It is possible that NGC 4262 has undergone a major gas stripping event in the past that was the origin of the present “necklace” of UV-bright knots.

LOCATING THE ACCRETION FOOTPRINT ON A HERBIG Ae STAR: MWC 480

Accretion is a fundamental process which establishes the dynamics of the protoplanetary disk and the final properties of the forming star. In solar-type stars, the star-disk coupling is determined by the magnetic field structure, which is responsible for funneling material from the disk midplane to higher latitudes on the star. Here, we use pan-chromatic data for the Herbig Ae star MWC 480 to address whether similar processes occur in intermediate-mass stars. MWC 480 has X-ray emission typical of actively accreting Herbig Ae stars, but with ~10× more photoelectric absorption than expected from optical and FUV data. We consider three sources for the absorption: the disk, absorption in a wind or jet, and accretion. While we detect the disk in scattered light in a re-analysis of archival Hubble Space Telescope data, the data are consistent with grazing illumination of the dust disk. We find that MWC 480's disk is stratified, geometrically thin, and is not responsible for the observed photoelectric absorption. MWC 480 drives a bipolar jet, but with a mass-loss rate that is low compared to other Herbig Ae stars, where the outflow is more favorably oriented and enhanced photoelectric absorption is not seen. This excludes a jet or wind origin for the enhanced photoelectric absorption. We compare MWC 480's O VI emission with other Herbig Ae stars. The distribution of the emission in inclination, and lack of a correlation of profile shape and system inclination excludes equatorially confined accretion for the FUSE Herbig Ae stars. The photoelectric absorption data further suggest that the accretion footprint on MWC 480 and other Herbig Ae stars is located at high-temperate, rather than polar, latitudes. These findings support the presence of funneled accretion in MWC 480 and Herbig Ae stars, strengthening the parallel to T Tauri stars.

Bridging galactic star formation from intermediate to local epochs

AbstractStarburst galaxies trace the star-formation history of the Universe throughout cosmological time. Several studies have shown that the star-formation-rate density of the Universe begins to steadily decline after the Universe had aged ~ 5.8 Gyr (redshifts z ~ 1). However, we do not yet fully understand the mechanism behind this shift in star formation at intermediate z. One possibility is that during this epoch galaxies underwent ‘downsizing,’ a shift in star formation being dominated by high- to lower-mass galaxies. Rest-frame ultraviolet (UV) observations of starburst galaxies reveal regions of young stellar clusters where massive O and B stars dominate the luminosity. Observations in the FUV (~ 1500 Å) can be used to detect starburst galaxies at z &lt; 1 because the bright end of the rest-frame FUV spectrum is not redshifted much, and is observable in the FUV filter. Alternatively, the rest-frame FUV light from starburst galaxies at higher redshifts is shifted to longer wavelengths and must be observed in redder filters. We present a study of the starburst population at intermediate z from FUV data taken with Hubble's Solar Blind Channel (SBC) of the Advanced Camera for Surveys (ACS). The number counts of FUV galaxies as a function of magnitude provide a direct statistical measure of the density and evolution of starbursts, and subsequently of the stellar clusters formed within these galaxies' environments. We present a comparison between the FUV starburst-galaxy counts at this epoch, and the local FUV counts of starbursts observed with GALEX.

Characterizing the Near‐UV Environment of M Dwarfs

We report the results of our HST snapshot survey with the ACS HRC PR200L prism, designed to measure the near-UV emission in a sample of nearby M dwarfs. 33 stars were observed, spanning the mass range from 0.1 - 0.6 solar masses (T_eff ~ 2200K - 4000K) where the UV energy distributions vary widely between active and inactive stars. These observations provide much-needed constraints on models of the habitability zone and the atmospheres of possible terrestrial planets orbiting M dwarf hosts, and will be useful in refining the target selection for future space missions such as TPF. We compare our data with a new generation of M dwarf atmospheric models and discuss their implication for the chromospheric energy budget. These NUV data will also be valuable in conjunction with existing optical, FUV and X-ray data to explore unanswered questions regarding the dynamo generation and magnetic heating in low-mass stars.

Evidence for significantly greater N2 Lyman‐Birge‐Hopfield emission efficiencies in proton versus electron aurora based on analysis of coincident DMSP SSUSI and SSJ/5 data

The launch of the Defense Meteorological Satellite Program (DMSP) satellite F16 in 2003 provided the first opportunity to analyze extensive sets of high‐quality coincident auroral particle and FUV data obtained by the onboard sensors Special Sensor Ultraviolet Spectrographic Imager (SSUSI) and Special Sensor Auroral Particle Sensor (SSJ/5). Features of interest are Ly α (121.6 nm), Lyman‐Birge‐Hopfield short (LBHS, the SSUSI 140–150 nm channel), and Lyman‐Birge‐Hopfield long (LBHL, 165–180 nm). We report on comparisons of column emission rates (CERs) by deriving simulated SSUSI values using SSJ/5 electron and ion (treated as proton) spectra. Field‐line tracing is performed to determine the locations of coincidences. CERs are obtained by integrating the products of particle spectra and monoenergetic emission yields. A technique is reported for deriving these yields from nonmonoenergetic CERs obtained by our particle transport model. SSJ/5 ion spectra are extrapolated above 30 keV using a statistical representation based on Polar Orbiting Environmental Satellites particle data. Key quantities of interest are ratios of SSUSI to SSJ/5‐based CERs (S‐S ratios) and corresponding ratios of proton‐produced to total emission (unity for Ly α and from 0 to 1 for LBHS and LBHL). SSJ/5‐based CERs are used to derive the latter ratios. Median ratio values are determined in order to reduce the error budget to primarily calibration and model errors. The median LBH S‐S ratios increase by a factor of ∼2.5 from electron to proton aurora and support significantly higher proton LBH emission efficiencies (3 times the electron efficiencies) assuming reported calibration uncertainties. This calls for significant increases in proton and/or H‐atom LBH cross sections. In turn, FUV auroral remote‐sensing algorithms must explicitly address both electron and proton aurora.