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NASA NTRS1991

First results from the Goddard High-Resolution Spectrograph - The chromosphere of Alpha Tauri

The K5 III star Alpha Tau was observed with the Goddard High Resolution Spectrograph on November 27, 1990 as part of the Science Assessment Program for the HST. The spectra show intersystem and permitted chromospheric emission lines of semiforbidden C II and Si II, Fe II, Fe I, Ni II, and Co II. Resolved profiles of the semiforbidden C II lines indicate a complex chromospheric turbulent velocity distribution with mean value of roughly 24 km/s, while their observed wavelengths indicate a 4 km/s downflow of the semiforbidden C II plasma. Twenty-five new emission lines have been found in the 2320-2370 A region, 17 of which have been identified with the aid of Skylab data obtained above the solar limb, including four lines from Co II (UV 8) and an Fe I (UV 12) line.

Carpenter, Kenneth G.↗

NASA NTRS1993

Models of symbiotic stars

One of the most important features of symbiotic stars is the coexistence of a cool spectral component that is apparently very similar to the spectrum of a cool giant, with at least one hot continuum, and emission lines from very different stages of ionization. The cool component dominates the infrared spectrum of S-type symbiotics; it tends to be veiled in this wavelength range by what appears to be excess emission in D-type symbiotics, this excess usually being attributed to circumstellar dust. The hot continuum (or continua) dominates the ultraviolet. X-rays have sometimes also been observed. Another important feature of symbiotic stars that needs to be explained is the variability. Different forms occur, some variability being periodic. This type of variability can, in a few cases, strongly suggest the presence of eclipses of a binary system. One of the most characteristic forms of variability is that characterizing the active phases. This basic form of variation is traditionally associated in the optical with the veiling of the cool spectrum and the disappearance of high-ionization emission lines, the latter progressively appearing (in classical cases, reappearing) later. Such spectral changes recall those of novae, but spectroscopic signatures of the high-ejection velocities observed for novae are not usually detected in symbiotic stars. However, the light curves of the 'symbiotic nova' subclass recall those of novae. We may also mention in this connection that radio observations (or, in a few cases, optical observations) of nebulae indicate ejection from symbiotic stars, with deviations from spherical symmetry. We shall give a historical overview of the proposed models for symbiotic stars and make a critical analysis in the light of the observations of symbiotic stars. We describe the empirical approach to models and use the observational data to diagnose the physical conditions in the symbiotics stars. Finally, we compare the results of this empirical approach with existing models and discuss unresolved problems requiring new observational and theoretical work.

Friedjung, Michael↗

NASA NTRS2016

First Results from Faint Infrared Grism Survey (Figs): First Simultaneous Detection of Ly Alpha Emission and Lyman Break From a Galaxy at Z =7.51

Galaxies at high redshifts provide a valuable tool to study cosmic dawn, and therefore it is crucial to reliably identify these galaxies. Here, we present an unambiguous and first simultaneous detection of both the Lyman-Alpha emission and the Lyman break from a z = 7.512 +/- 0.004 galaxy, observed in the Faint Infrared Grism Survey (FIGS). These spectra, taken with G102 grism on Hubble SpaceTelescope (HST), show a significant emission line detection (6 Sigma) in two observational position angles (PA), with Lyman-Alpha line flux of 1.06 +/- 0.19 x 10(exp -17) erg s(exp -1) cm(exp -2). The line flux is nearly a factor of four higher than in the archival MOSFIRE spectroscopic observations. This is consistent with other recent observations implying that ground-based near-infrared spectroscopy underestimates total emission line fluxes, and if confirmed, can have strong implications for reionization studies that are based on ground-based Lyman-Alpha measurements. A 4-Alpha detection of the NV line in one PA also suggests a weak Active Galactic Nucleus (AGN), and if confirmed would make this source the highest-redshift AGN yet found.These observations from the Hubble Space Telescope thus clearly demonstrate the sensitivity of the FIGS survey, and the capability of grism spectroscopy to study the epoch of reionization.

Faint Galaxy Z=7.51↗

DOE OSTI2022

The Chocolate Chip Cookie Model: Dust Geometry of Milky Way–like Disk Galaxies

We present a new two-component dust geometry model, the Chocolate Chip Cookie model, where the clumpy nebular regions are embedded in a diffuse stellar/interstellar medium disk, like chocolate chips in a cookie. By approximating the binomial distribution of the clumpy nebular regions with a continuous Gaussian distribution and omitting the dust scattering effect, our model solves the dust attenuation process for both the emission lines and stellar continua via analytical approaches. Our Chocolate Chip Cookie model successfully fits the inclination dependence of both the effective dust reddening of the stellar components derived from stellar population synthesis and that of the emission lines characterized by the Balmer decrement for a large sample of Milky Way–like (MW-like) disk galaxies selected from the main galaxy sample of the Sloan Digital Sky Survey. Our model shows that the clumpy nebular disk is about 0.55 times thinner and 1.6 times larger than the stellar disk for MW-like galaxies, whereas each clumpy region has a typical optical depth of τ cl,V ~ 0.5 in the V band. After considering the aperture effect, our model prediction on the inclination dependence of dust attenuation is also consistent with observations. Not only that, in our model, the dust attenuation curve of the stellar population naturally depends on the inclination, and its median case is consistent with the classical Calzetti law. As the modeling constraints are from the optical wavelengths, our model is unaffected by the optically thick dust component, which however could bias the model's prediction of the infrared emissions.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1993

HST/FOS spectra of PG 1351+64: An intrinsic absorber at low redshift

A 1 A resolution spectra of the nearby (z = 0.08797) Seyfert galaxy PG 1351+64 taken with the Faint Object Spectrograph (FOS) onboard the Hubble Space Telescope is presented. Spectral coverage runs from 1200-3200 A in the observed frame and includes emission and absorption features due to Ly-alpha, N 5, Si 4, C 4, and Mg 2. Three distinct intrinsic absorption systems in Ly-alpha, N 5, Si 4, and C 4, and tentatively in Mg 2, at velocities of 900 km/s, 1630 km/s, and 2900 km/s (plus or minus 100 km/s) relative to the emission-line redshift of the QSO were detected. The maximum relative velocity of these absorbers is less than 5000 km/s and therefore does not meet Weymann, Carswell, & Smith's criteria for Broad-Absorption-Line (BAL) QSO's at high-z. However, the absorptions are almost certainly intrinsic to the QSO given the low redshift of this object. In addition, PG 1351+64 is marginally radio-quiet, as are all BALQSO's, based on recent estimates of the radio-loud/radio-quiet dividing line. The narrow velocity width, less than 500 km/s, and low outflow velocities of the absorption systems are more similar to so called 'associated absorbers' seen at high-z in radio-loud quasars, but whose absorptions are thought to arise in clouds much farther from the nucleus (greater than 1 kpc) than are BAL clouds (1-10 pc). Despite the qualitative resemblance to the associated absorbers, the absorption systems in PG 1351+64 appear to be the low-luminosity analogs of BALQSO absorption troughs. The lower observed outflow velocities in PG 1351+64 are due to the much lower luminosity of the nuclear source in comparison to the high-z, high-luminosity BALQSO's. In addition, 'satellite' emission lines displaced 4000-5000 km/s blueward and redward of the Mg 2 emission were discovered.

Granados, Arno↗

NASA NTRS2016

The Muscles Treasury Survey. I. Motivation and Overview

Ground- and space-based planet searches employing radial velocity techniques and transit photometry have detected thousands of planet-hosting stars in the Milky Way. With so many planets discovered, the next step toward identifying potentially habitable planets is atmospheric characterization. While the Sun-Earth system provides a good framework for understanding the atmospheric chemistry of Earth-like planets around solar-type stars, the observational and theoretical constraints on the atmospheres of rocky planets in the habitable zones (HZs) around low-mass stars (K and M dwarfs) are relatively few. The chemistry of these atmospheres is controlled by the shape and absolute flux of the stellar spectral energy distribution (SED), however, flux distributions of relatively inactive low-mass stars are poorly understood at present. To address this issue, we have executed a panchromatic (X-ray to mid-IR) study of the SEDs of 11 nearby planet-hosting stars, the Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems (MUSCLES) Treasury Survey. The MUSCLES program consists visible observations from Hubble and ground-based observatories. Infrared and astrophysically inaccessible wavelengths (EUV and Lyalpha) are reconstructed using stellar model spectra to fill in gaps in the observational data. In this overview and the companion papers describing the MUSCLES survey, we show that energetic radiation (X-ray and ultraviolet) is present from magnetically active stellar atmospheres at all times for stars as late as M6. The emission line luminosities of C IV and Mg II are strongly correlated with band-integrated luminosities and we present empirical relations that can be used to estimate broadband FUV and XUV (is equivalent to X-ray + EUV) fluxes from individual stellar emission line measurements. We find that while the slope of the SED, FUV/NUV, increases by approximately two orders of magnitude form early K to late M dwarfs (approximately equal 0.01-1), the absolute FUV and XUV flux levels at their corresponding HZ distances are constant to within factors of a few, spanning the range 10-70 erg per (sq cm) s in the HZ. Despite the lack of strong stellar activity indicators in their optical spectra, several of the M dwarfs in our sample show spectacular UV flare emission in their light curves. We present an example with flare/quiescent ultraviolet flux ratios of the order of 100:1 where the transition region energy output during the flare is comparable to the total quiescent luminosity of the star E(sub flare)(UV) approximately 0.3 L(sub *) delta (t) (delta t = 1 s). Finally, we interpret enhanced L(line)/L(sub Bol) ratios for C IV and N V as tentative observational evidence for the interaction of planets with large planetary mass-to-orbital distance ratios (M(sub plan)/A(sub plan)) with the transition regions of their host stars.

Infrared and astrophysically inaccessible waveleng↗

NASA NTRS1988

4C 40.36 - A radio galaxy at a redshift of 2.3

Long-slit spectroscopy of a faint extended optical object identified with the radio source 4C 40.36 is presented. Three emission lines are detected. Their wavelengths match those of C IV 1549 A, He II 1640 A, and semiforbidden C III 1909 A to within 0.5 percent for a redshift of z = 2.269. The extended continuum emission (20 kpc) together with the large equivalent widths (about 100 A) and narrow profiles (1500 km/s) of the emission lines, all show that 4C 40.36 is a galaxy with properties similar to those of other distant radio galaxies. The redshift of 4C 40.36, however, considerably exceeds that of the most distant radio galaxy (3C 326.1 at z = 1.825) known to date. 4C 40.36 is of additional interest as an excellent example of the recently discovered phenomenon of alignment between the optical and radio axes of powerful distant radio galaxies. The object was investigated as part of a survey of ultra-steep spectrum radio sources, and it is shown that the selection criteria used to discover 4C 40.36 result in a sample of objects having a relatively low dispersion of monochromatic radio luminosities.

Chambers, K. C.↗

NASA NTRS1988

Simultaneous IUE, EXOSAT and optical observations of the unusual AM Her type variable H058+608

Simultaneous observations of the AM Her type variable H0538+608 made with IUE, EXOSAT, and a 1.3 m ground based telescope, and subsequent optical spectrophotometry at high and low resolution are discussed. The X-ray and optical data show clear evidence of a 3.30 + or - 0.03 hr period. Three SWP spectra were taken outside of eclipse and during overlapping phase intervals. The UV spectra contain strong emission lines characteristic of this class of objects and a flat continuum which appears to be deficient, given the brightness of source at optical and X-ray wavelengths. There is evidence for intensity variations in emission lines, particularly C IV. The X-ray light curves for H0538+608 reveal behavior which may be related to irregularities in its accretion flow.

Shrader, C. R.↗

NASA NTRS1992

The first linear polarization spectra of Wolf-Rayet stars in the ultraviolet - EZ Canis Majoris and Theta Muscae

During the 1990 December Astro-1 Space Shuttle mission, spectropolarimetry was conducted in the wavelength region from 1400 to 3200 A of the Wolf-Rayet stars EZ CMa (WN5) and Theta Mus (WC6 + O9.5I) with the Wisconsin Ultraviolet Photo-Polarimeter Experiment. The UV polarization of EZ CMa displays features which correspond to emission lines. This indicates a large, about 0.8 percent, intrinsic UV-continuum polarization, and provides further evidence that the wind of EZ CMa is highly distorted. The polarization of Theta Mus does not change across emission lines, or the strong interstellar 2200 A feature. The polarization decreases smoothly to shorter wavelengths, at constant position angle. The combined UV-optical polarization spectrum of Theta Mus can be described well with interstellar polarization following a Serkowski law.

Schulte-Ladbeck, R. E.↗

NASA NTRS1992

X-ray FE line studies

We present the first broadband, moderate-resolution X-ray spectral observations of the Seyfert galaxies NGC 4151 and NGC 1068. The Seyfert 1 galaxy NGC 4151 is shown to have a complex X-ray spectrum with multiple components and a strong, intrinsically narrow Fe K emission line. The characteristics of the scattering medium of the Seyfert 2 galaxy NGC 1068 are determined using the very strong Fe line emission and the lack of features due to oxygen in the X-ray spectrum. The soft X-ray flux from Mrk 3 and Mrk 348 are consistent with that expected from electron scattered X-rays from an obscured Seyfert 1 nucleus. A survey of the X-ray properties of Seyfert 2 galaxies indicates that a substantial fraction may have column densities of about 10 exp 23, suggesting that NGC 1068 has an unusually thick obscuring torus.

Marshall, F. E.↗

NASA NTRS1996

Results of Detailed Modeling of the Narrow-Line Region of Seyfert Galaxies

We present model line profiles of [O II] lambda3727, [Ne III] lambda3869, [O I] lambda5007, [Fe VII] lambda6087, [Fe X] lambda6374, [O I] lambda6300, H(alpha) lambda6563, and [S 2] lambda6731. The profiles presented here illustrate explicitly the pronounced effects that collisional de-excitation, and that spatial variations in both the ionization parameter and cloud column density, have on Narrow-Line Region (NLR) model profiles. The above effects were included only qualitatively in a previous analytical treatment by Moore and Cohen. By making a direct correspondence between these model profiles and the analytical model profiles of Moore and Cohen, and by comparing with the observed profiles presented in a companion paper and also with those presented elsewhere in the literature, we strengthen some of the conclusions of Moore and Cohen. Most notably, we argue for constant ionization parameter, uniformly accelerated outflow of clouds that are individually stratified in ionization, and the interpretation of emission-line width correlations with ionization potential as a column density effect. For comparison with previous observational studies, such as our own in a companion paper, we also calculate profile parameters for some of the models, and we present and discuss the resulting line width correlations with critical density (n(sub cr)) and Ionization Potential (IP). Because the models we favor are those that produce extended profile wings as observed in high spectral resolution studies, the line width correlations of our favoured models are of particular interest. Line width correlations with n(sub cr) and/or IP result only if the width parameter is more sensitive to extended profile wings than is the Full Width at Half-Maximum (FWHM). Correlations between FWHM and n(sub cr) and/or IP result only after convolving the model profiles with a broad instrumental profile that simulates the lower spectral resolution used in early observational studies. The model in agreement with the greatest number of observational considerations has electron density decreasing outward from n(sub e) approx. equals 10(exp 6)/cu cm to n(sub e) approx. equals 10(exp 2)/cu cm and, due to collisional de-excitation effects in the lowest velocity clouds, it generates broad flat-topped profile peaks in the lines of lowest critical density (e.g., [O II] lambda3727 and [S II] lambda(lambda)6716, 6731). Because the observed profile peaks of both low and high critical density lines are often very similar, our favored model requires a contribution to NLR emission-line spectra from low-velocity, low-density, and low-ionization gas not included in the model NLR.

Moore, David↗

DOE OSTI2023

Ferricyanide photo-aquation pathway revealed by combined femtosecond Kβ main line and valence-to-core x-ray emission spectroscopy

Reliably identifying short-lived chemical reaction intermediates is crucial to elucidate reaction mechanisms but becomes particularly challenging when multiple transient species occur simultaneously. Here, we report a femtosecond x-ray emission spectroscopy and scattering study of the aqueous ferricyanide photochemistry, utilizing the combined Fe Kβ main and valence-to-core emission lines. Following UV-excitation, we observe a ligand-to-metal charge transfer excited state that decays within 0.5 ps. On this timescale, we also detect a hitherto unobserved short-lived species that we assign to a ferric penta-coordinate intermediate of the photo-aquation reaction. We provide evidence that bond photolysis occurs from reactive metal-centered excited states that are populated through relaxation of the charge transfer excited state. Beyond illuminating the elusive ferricyanide photochemistry, these results show how current limitations of Kβ main line analysis in assigning ultrafast reaction intermediates can be circumvented by simultaneously using the valence-to-core spectral range.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1995

Near-infrared and optical spectroscopy of FSC 10214+4724

New infrared and optical spectroscopic observations, obtained with the W. M. Keck Telescope, are reported for the highly luminous infrared source FSC 10214+4724. The rest frame optical spectrum shows new emission lines of (Ne III), (Ne V), (O I), (O II), (S II), and He(+), while the rest frame ultraviolet spectrum shows new lines of O IV) + Si IV, N III, N IV), Si II, Ne IV, and possibly N II and (Ne III), as well as clearly showing that Ly-alpha is self-absorbed. The emission-line spectrum is most characteristic of a Seyfert 2 nucleus. The preponderance of spectroscopic evidence strengthens the case for a dust-enshrouded Active galactic nuclei (AGN) powering much or most of the observed luminosity. The various spectral lines lead to a wide range in the inferred reddening and ionization parameter for this system, suggesting that we are viewing several environments through differing extinctions.

Soifer, B. T.↗

NASA NTRS1988

Rotational modulation and flares on RS CVn and BY Dra stars

Evidence is presented for spots, plages, and flares on the noneclipsing RS CVn system II Peg and V 711 Tau. The large spot originally found on II Peg in 1981.8 could still be identified in 1983. Two spectroscopic flares of II Peg were detected. For the larger flare the fluxes in the strongest transition-region lines reached about six times their quiescent values. A comparison of the 1981 and 1983 flux variations show that active regions or plages are located on one hemisphere. On V 711 Tau at least two flares were observed. Outside of these flares, the strongest chromospheric and transition-region emission lines exhibited weak phase-dependent variations that persist over 173 orbital cycles (1981-1983) and are possibly associated with one of the proposed spots. For both stellar systems the fluxes from the higher temperature emission lines showed the greatest variations.

Andrews, A. D.↗

NASA NTRS2005

Stellar Activity and Mass Loss from A and F Supergiants

This grant supported the observing and data analysis for FUSE Cycle 4 project DO47 to observe five late-A and F supergiants using a total observing allocation of 150 ksec. Stellar activity on A and F supergiants has been poorly studied in the past; primarily because the photospheric continuum dominates any chromospheric (~ 10 4 K) or transition region (TR; ~ 10 5 K) emission lines far into the ultraviolet. FUSE observations of A and F supergiants offer one of the best methods to study stellar activity on these stars, because many activity indicators longward of 1200 A are swamped by the photospheric continuum emission. We used FUSE FUV spectra to search for 0 VI and C I11 TR emission lines and obtained data for t Car (A8 Ib, for 60.5 ksec, on 2003 Apr 27), 8 Sco (F1 11, 22.7 ksec, 2003 Aug 2), ct Per (F5 Ib, 30.8 ksec, 2003 Oct l), a UMi (F7 Ib-11, 23.9 ksec, 2003 Oct 14), and y Cyg (F8 Ib, 25.8 ksec, 2003 Oct 18). These observations used the large LWRS aperture and collected data in time-tagged mode. The LWRS aperture is large enough that the target should remain within the aperture with the normal level of FUSE pointing jitter and target drift. We examined the stellar signal and found that the targets were well within the aperture throughout the observation. The data were split into night-time and day-time data so that the effects of airglow emission were recognizable, and combined day and night spectra were generated using CALFUSE 2.4.0 .

Brown, Alexander↗

NASA NTRS1981

Are we beginning to understand T Tauri stars

An international meeting of astronomers in April 1981 in Portugal to discuss recent data on T Tauri stars is described. It is pointed out that T Tauri stars all vary irregularly in brightness, occur in intimate association with dusty molecular clouds, and exhibit bright optical emission lines, principally of hydrogen, helium, and iron. Stars with masses roughly 0.2 to three times the sun's and with ages from 100,000 to 1,000,000 years are typical of the T Tauri regime. It is thought that the often rich emission-line spectra seen at visible wavelengths indicate the presence of a stellar chromosphere, where the temperature rises steeply from the usual cool photospheric values around 4,000 to 5,000 K. Even though a recent extensive survey of T Tauri stars has been completed, no clear role for rotation in producing radio emission or stellar winds has yet emerged.

Cohen, M.↗

NASA NTRS1992

Faint object spectrograph observations of the large-redshift gravitational lens candidate 1208+1011

HST spectroscopic observations of 3.8-redshift gravitational lens candidate 1208+1011 are reported. Low-dispersion Faint Object Spectrograph data covering the wavelength range 3700-7800 A are obtained for each of the two components and for a comparison field; the fainter component and the black field are both separated by 0.47 arcsec from the brighter image. The spectra of both components possess strong Ly-alpha/N V and O VI/Ly-beta emission lines at a redshift of 3.8 as well as a number of similar absorption features. Both components have a ratio of the equivalent widths of the O VI complex to the Ly-alpha complex much larger than the typical value seen in large-redshift quasars. The small differences in the measured profiles of the Ly-alpha and O VI/Ly-beta emission lines of the images could be caused by absorption along different paths to a single lensed object, by unequal imaging of extended emissions, by systematic measuring errors, or by intrinsic differences in two nearly identical neighboring quasars.

Bahcall, John N.↗

NASA NTRS1983

X-ray, optical, and radio observations of the blue galaxy Butcher-Oemler 6 in the 3C 295 cluster

The nature of the blue members of distant, condensed clusters of galaxies are investigated through X ray, optical, and radio observations of the brightest such object in the 3C 295 cluster. The X ray luminosity and the optical emission line spectrum show that this galaxy is a Seyfert, in contrast to the original suggestion that the blue galaxies are rapidly evolving spirals. The observations yield an X ray luminosity of 3.4 x 10 to the 44th ergs/sec (0.5-4.5 keV), strong optical emission lines of Mg II and forbidden O II at a redshift of 0.473, and an upper limit to the radio luminosity at 20 cm of 7.0 x 10 to the 24th W/Hz. Compared to other Seyfert galaxies, this object appears relatively X ray luminous, shows an average Mg II/X ray flux ratio, and is relatively weak in H-beta emission.

Lavery, R. J.↗