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NASA NTRS1984

Ultraviolet observations of the Be star Mu Centauri during its recent active phase

IUE and Copernicus ultraviolet observations and ground-based image-tube and direct spectrograms of the pole-on Be star Mu Cen have been combined to investigate the nature of this star's activity during its Balmer emission-line episode of 1980-81. Within the uncertainties of the observations, the UV data show no evidence for a wind, a classical-type shell injection, or a region of superionization, either before, during, or after the active phase. This is contrary to current views on how the circumstellar envelopes in Be stars are produced. The only difference between the UV spectra observed during activity and quiescence was that the lines from the more highly ionized species (e.g., Si III, Si IV, Al III) were slightly stronger and broader when Balmer emission was present. Evidence is presented that the activity most likely resides in or near the photosphere, and that during such active periods the photospheric temperature is higher. The recently discovered nonradial pulsations in Mu Cen (Baade, 1984) may supply the energy. The lack of sharp or broad shell lines in the UV suggests that the Balmer emission envelope is at least somewhat flattened.

Peters, G. J.↗

NASA NTRS1988

Line variability and the broad emission line region of quasi-stellar objects. II - Changes in Balmer decrements

Evidence is presented for significant variations of broad emission lines in five QSOs supporting an earlier report by Zheng et al. (1987). The Balmer decrements before and after variations are compared in an effort to extract information on the broad-line regions. The broad hydrogen lines are found to vary in step with the underlying continuum, indicating that the continuum is the probable energy source for emission lines. The ratios of H-beta/H-alpha for both the varying and steady parts of the the broad lines are about 0.2, suggesting that the regions in which these line fluxes originate are exposed to similar ionizing flux and are therefore at about the same distance to the central source. The average ratio of H-gamma/H-beta is 0.8 for the variable components, considerably higher than that of the constant components. Thus, the region producing the varying line fluxes may have higher density and lower optical depth.

Zheng, Wei↗

NASA NTRS1982

Optical identification of Balmer-dominated supernova remnants in the Large Magellanic Cloud

Optical emission-line images are presented for four SNR's that are luminous X-ray sources and that were recently discovered during an X-ray survey of the LMC. The images reveal distinct filamentary shells that are prominent in the Balmer lines of H but are either absent or very weak in forbidden O III and forbidden S II emission. One remnant exhibits clear evidence for velocity-broadened H-alpha emission, and all four are expanding into regions with a relatively low H I density. It is shown that both the broad H-alpha emission and the Balmer-dominated spectra can be understood in terms of a very high-velocity nonradiative shock encountering gas that is partially neutral. The optical, X-ray, and radio properties of the LMC remnants are compared with those of relatively young galactic SNR's. It is concluded that all four LMC remnants resulted from Type I supernovae.

Tuohy, I. R.↗

NASA NTRS1992

EC 19314 - 5915 - A bright, eclipsing cataclysmic variable from the Edinburgh-Cape Blue Object Survey

A deeply eclipsing cataclysmic variable, with an orbital period of 4.75 hr, has been discovered in the southern Edinburgh-Cape Blue Object Survey. The star, EC 19314 - 5915, lies close to the positional constraints of a previously unidentified HEAO-1 hard X-ray source, 1H1930 - 5989. Its optical spectrum is unusual in that it shows, apart from the emission lines characteristic of a novalike, or dwarf nova cataclysmic variable (Balmer, He I and He II), metallic absorption lines typical of a late-G star. The individual time-resolved spectra, with the tertiary absorption lines removed, show absorption reversals in the Balmer emission lines, increasing in strength for the higher series. The Balmer emission radial velocities are therefore severely distorted in comparison to the He II 4686-A emission and He I 4471-A absorption radial velocity curves. An independent distance estimate of about 600 pc is derived for EC19314 - 5915, from the spectroscopic parallax of the third star.

Buckley, D. A. H.↗

NASA NTRS2019

Spatially Resolved Outflows in a Seyfert Galaxy at z=2.39

We present the first spatially resolved analysis of rest-frame optical and UV (UltraViolet) imaging and spectroscopy for a lensed galaxy at z equals 2.39 hosting a Seyfert active galactic nucleus (AGN). Proximity to a natural guide star has enabled observations with high signal-to-noise ratio using Very Large Telescope SINFONI (Spectrograph for INtegral Field Observations in the Near Infrared) plus adaptive optics (AO) of rest-frame optical diagnostic emission lines, which exhibit an underlying broad component with full width at half maximum approximately 700 kilometers per second in both the Balmer and forbidden lines. Measured line ratios place the outflow robustly in the region of the ionization diagnostic diagrams associated with AGNs. This unique opportunity - combining gravitational lensing, AO guiding, redshift, and AGN activity - allows for a magnified view of two main tracers of the physical conditions and structure of the interstellar medium in a star-forming galaxy hosting a weak AGN at Cosmic Noon. By analyzing the spatial extent and morphology of the Lyman alpha spectral line and dust-corrected Hydrogen spectral line emission, disentangling the effects of star formation and AGN ionization on each tracer, and comparing the AGN-induced mass outflow rate to the host star formation rate, we find that the AGN does not significantly impact the star formation within its host galaxy.

Fischer, Travis C.↗

NASA NTRS1989

Evidence for a high-mass white dwarf in nova V1500 Cygni 1975

Time-resolved spectroscopy of V1500 Cyg are presented from 1981, when the nebular lines from the nova ejecta had faded sufficiently to permit reliably radial velocity measurements on emission lines from the binary remnant. The spectra possess a typical AM Herculis signature. The wavelength region 3800-5100 A contains a number of strong lines, in particular the Balmer series and He II 4686 A. All lines show periodic velocity changes with the same period as the photometric variations. On the first night the lines are relatively weak and narrow, are in phase with the photometric cycle, and suffer extreme modulation; two months later they are strong and broad, are roughly 90 deg out of phase with the photometric cycle, and have relatively less variation in their line fluxes. These features support the suggestion that the remnant is an AM Her system. The observed radial velocity of the secondary is 193 + or - 9 km/s. Various constraints suggest that the magnetic white dwarf in this system has a mass over 0.9 solar.

Horne, Keith↗

DOE OSTI2021

A comprehensive chemical abundance analysis of the extremely metal poor Leoncino Dwarf galaxy (AGC 198691)

ABSTRACT We re-examine the extremely metal-poor dwarf galaxy AGC 198691 using a high quality spectrum obtained by the LBT’s MODS instrument. Previous spectral observations obtained from KOSMOS on the Mayall 4-m and the Blue channel spectrograph on the MMT 6.5-m telescope did not allow for the determination of sulfur, argon, or helium abundances. We report an updated and full chemical abundance analysis for AGC 198691, including confirmation of the extremely low “direct” oxygen abundance with a value of 12 + log (O/H) = 7.06 ± 0.03. AGC 198691’s low metallicity potentially makes it a high value target for helping determine the primordial helium abundance (Yp). Though complicated by a Na i night sky line partially overlaying the He i λ5876 emission line, the LBT/MODS spectrum proved adequate for determining AGC 198691’s helium abundance. We employ the recently expanded and improved model of Aver et al., incorporating higher Balmer and Paschen lines, augmented by the observation of the infrared helium emission line He i λ10830 obtained by Hsyu et al. Applying our full model produced a reliable helium abundance determination, consistent with the expectation for its metallicity. Although this is the lowest metallicity object with a detailed helium abundance, unfortunately, due to its faintness [EW(Hβ) < 100 Å] and the compromised He i λ5876, the resultant uncertainty on the helium abundance is too large to allow a significant improvement on the measurement of Yp.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2020

Periodic Eruptive Variability of the Isolated Pre-main-sequence Star V347 Aurigae

V347 Aurigae is associated with the small dark cloud L1438 and appears to be an isolated pre-main-sequence star located at distance d ≈ 200 pc. Multi-epoch, archival photometry reveals periodic brightness variations with amplitude V ≈ 2.0 mag occurring on timescales of ~160 days that have persisted for decades. Regular-cadence, optical imaging of the source with the Zwicky Transient Facility shows that a small reflection nebula illuminated by V347 Aur also fluctuates in brightness, at times fading completely. Multi-epoch, Keck/HIRES data suggests the presence of two distinct spectral components: a prominent emission-line-dominated spectrum with a heavily veiled continuum correlated with the bright photometric state, and an M-type absorption line spectrum associated with quiescence. All spectra exhibit strong Balmer and He i line emission, consistent with accretion, as well as high velocity emission arising from the forbidden transitions of [O i], [N ii], and [S ii] that are generally associated with collimated jets and disk winds. There is no evidence in existing high-dispersion spectroscopy or high-resolution imaging for binarity of V347 Aur. The repeating outburst events are possibly linked to accretion instabilities induced by an undetected companion or a structure within the circumstellar disk that periodically increases the mass accretion rate. V347 Aur is perhaps analogous to an EXor-type variable, though more regularly recurring.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1982

A spectrophotometric survey of cataclysmic variable stars

A sample of dwarf novae and other cataclysmic variable stars were observed using the multichannel spectrophotometer on the 5-m Hale reflector. A preliminary qualitative description of the continuum distributions is given and a discussion of the Balmer emission-line fluxes is made. For the spectral energy distributions, the logarithm of the monochromatic flux density is plotted against the inverse of the wavelength. It is concluded that the presence or absence of evident flux from a late-type stellar component is consistent with the standard picture which has been developed for the structure of cataclysmic variable stars. The presence of the Balmer jump in emission or absorption can be understood in terms of the relative importance of an optically thick accreting disk characteristic of nova-like variables and dwarf novae in outburst and an optically thin outer accreting disk characteristic of quiescent dwarf novae.

Oke, J. B.↗

DOE OSTI2026

Identifying Anomalous DESI Galaxy Spectra with a Variational Autoencoder

The tens of millions of spectra being captured by the Dark Energy Spectroscopic Instrument (DESI) provide tremendous discovery potential. In this work we show how Machine Learning, in particular Variational Autoencoders (VAE), can detect anomalies in a sample of approximately 200,000 DESI spectra comprising galaxies, quasars and stars. We demonstrate that the VAE can compress the dimensionality of a spectrum by a factor of 100, while still retaining enough information to accurately reconstruct spectral features. We then detect anomalous spectra as those with high reconstruction error and those which are isolated in the VAE latent representation. The anomalies identified fall into two categories: spectra with artefacts and spectra with unique physical features. Awareness of the former can help to improve the DESI spectroscopic pipeline; whilst the latter can lead to the identification of new and unusual objects. To further curate the list of outliers, we use the Astronomaly package which employs Active Learning to provide personalised outlier recommendations for visual inspection. In this work we also explore the VAE latent space, finding that different object classes and subclasses are separated despite being unlabelled. We demonstrate the interpretability of this latent space by identifying tracks within it that correspond to various spectral characteristics. For example, we find tracks that correspond to increasing star formation and increase in broad emission lines along the Balmer series. In upcoming work we hope to apply the methods presented here to search for both systematics and astrophysically interesting objects in much larger datasets of DESI spectra.

Nicolaou, C. [University Coll. London] (ORCID:0000↗

NASA NTRS1982

Changes in the UV spectrum of HD 4174

It is noted that the symbiotic-like object HD 4174 (EG And) exhibits the optical spectrum of an M2 giant star, but also shows Balmer and nebular line emission. The first UV spectrum showed an intense far UV emission line spectrum typical of many symbiotic stars. A 470 day binary or pulsation period for this system, based on the changing strength and velocity of the H alpha emission. Preliminary indications are that the H alpha and far UV continuum are eclipsed near phase 0.6 (at maximum H alpha redshift), but that the correlation for the emission lines remains unclear and requires additional observations.

Stencel, R. E.↗

NASA NTRS1985

The ultraviolet excess of quasars 3: The highly polarized quasars PKS 0736+017 and PKS 1510-089

Ultraviolet/optical/infrared spectrophotometry of the highly-polarized quasars (HPQ's) PKS 0736+017 and PKS 1510-089 is analyzed. A blazar continuum component like that in BL Lac objects (e.g. with violent variability, high polarization, and a steep power-law shape) contributes about half the visual light of 1510-089, and at least three-quarters of that in 0736+017. The remaining light has the same spectrum as normal (low-polarization) quasars, including an ultraviolet excess or blue bump, which is easily detected in the IUE spectra of 1510-089, and weakly detected in 0736+017. The line fluxes do vary, but not as much as the continuum. The ratios of the broad emission lines, and the Balmer continuum are normal in both quasars.

Malkan, M. A.↗

NASA NTRS1986

The ultraviolet excess of quasars. III - The highly polarized quasars PKS 0736 + 017 and PKS 1510 - 089

Ultraviolet/optical/infrared spectrophotometry of the highly-polarized quasars (HPQ's) PKS 0736 + 047 and PKS 1510 089 is analyzed. A blazer continuum component like that in BL Lac objects (e.g. with violent variability, high polarization, and a steep power-law shape) contributes about half the visual light of 1510 - 089, and at least three-quarters of that in 0736 + 017. The remaining light has the same spectrum as normal (low-polarization) quasars, including an ultraviolet excess or blue bump, which is easily detected in the IUE spectra of 1510 - 089, and weakly detected in 0736 + 017. The line fluxes do vary, but not as much as the continuum. The ratios of the broad emission lines, and the Balmer continuum are normal in both quasars.

Malkan, M. A.↗

NASA NTRS1990

Velocity mapping in the plume of a 30-kW ammonia arcjet

The flow velocity of atomic hydrogen in the plume of an ammonia-propelled arcjet was measured using LIF. The velocity was obtained by the Doppler shift of the absorption peak of the Balmer alpha spectral line. Measurements were made at the nozzle exit, varying the distance from the plume centerline. Results are presented for arcjet operating conditions 13, 20 and 27 kW with a mass flow of 0.31 g/s. The on-axis H flow velocity varies from 14 km/s to 28 km/s over this range of input power. The axial velocity as a function of the distance from the axis is sharply peaked, dropping to almost zero at a radius of less than 5 mm.

Pham-Van-diep, Gerald C.↗

NASA NTRS2006

Observations of the Hot Horizontal Branch Stars in the Metal-Rich Bulge Globular Cluster NGC 6388

The metal-rich bulge globular cluster NGC 6388 shows a distinct blue horizontal-branch tail in its colour-magnitude diagram (Rich et al. 1997) and is thus a strong case of the well-known 2nd Parameter Problem. In addition, its horizontal branch (HB) shows an upward tilt toward bluer colours, which cannot be explained by canonical evolutionary models. Several non-canonical scenarios have been proposed to explain these puzzling observations. In order to test the predictions of these scenarios, we have obtained medium resolution spectra to determine the atmospheric parameters of a sample of the blue HB stars in NGC 6388.Using the medium resolution spectra, we determine effective temperatures, surface gravities and helium abundances by fitting the observed Balmer and helium lines with appropriate theoretical stellar spectra. As we know the distance to the cluster, we can verify our results by determining masses for the stars. During the data reduction we took special care to correctly subtract the background, which is dominated by the overlapping spectra of cool stars. The cool blue tail stars in our sample with T(sub eff) approximately 10000 K have lower than canonical surface gravities, suggesting that these stars are, on average, approximately equal to 0.4 mag brighter than canonical HB stars in agreement with the observed upward slope of the HB in NGC 6388. Moreover, the mean mass of these stars agrees well with theoretical predictions. In contrast, the hot blue tail stars in our sample with T(sub eff) greater than or equal to 12000 K show significantly lower surface gravities than predicted by any scenario, which can reproduce the photometric observations. Their masses are also too low by about a factor of 2 compared to theoretical predictions. The physical parameters of the blue HB stars at about 10,000 K support the helium pollution scenario. The low gravities and masses of the hot blue tail stars, however, are probably caused by problems with the data reduction, most likely due to remaining background light in the spectra, which would affect the fainter hot blue tail stars much more strongly than the brighter cool blue tail stars. Our study of the hot blue tail stars in NGC 6388 illustrates the obstacles which are encountered when attempting to determine the atmospheric parameters of hot HB stars in very crowded fields using ground-based observations. We discuss these obstacles and offer possible solutions for future projects.

Moehler, S.↗

NASA NTRS2004

The Companion to the Central Mira Star of the Protoplanetary Nebula OH 231.8+4.2

We present deep optical long-slit spectra of the peculiar protoplanetary nebula (PPN) OH 231.8+4.2 obtained with the 6.5 m Baade Telescope at Las Campanas Observatory (Chile). In addition to the molecular absorption bands characteristic of the M9-10 III star inside OH 231.8+4.2 (QX Pup), we identify lines of the Balmer series in absorption, which do not form in the cool atmospheres of late M-type stars. We also confirm the presence of a blue continuum excess with an intensity that is a factor 30 larger than that expected for an M9-10 III star. Our results indicate the presence of a source hotter than QX Pup illuminating OH 231.8+4.2 that is likely a main-sequence star with spectral type A. We discuss how the formation and nebular evolution of OH 231.8+4.2 could have been affected by the presence of a binary system in its core.

binaries↗

NASA NTRS2017

Suppression of Hydrogen Emission in an X-Class White-Light Solar Flare

We present unique NUV observations of a well-observed X-class flare from NOAA 12087 obtained at the Ondrejov Observatory. The flare shows a strong white-light continuum but no detectable emission in the higher Balmer and Lyman lines. Reuven Ramaty High-Energy Solar Spectroscopic Imager and Fermi observations indicate an extremely hard X-ray spectrum and gamma-ray emission. We use the RADYN radiative hydrodynamic code to perform two types of simulations: one where an energy of 3 x 10(exp 11) erg/sq cm/s is deposited by an electron beam with a spectral index of approx. = 3, and a second where the same energy is applied directly to the photosphere. The combination of observations and simulations allows us to conclude that the white-light emission and the suppression or complete lack of hydrogen emission lines is best explained by a model where the dominant energy deposition layer is located in the lower layers of the solar atmosphere, rather than the chromosphere.

Prochazka, Ondrej↗

NASA NTRS1984

NGC 7213 - A key to the nature of liners?

New optical spectra of the nearby S0 galaxy NGC 7213 are analyzed. The observations are described and a brief overview of the spectrum is given. The subtraction of the stellar component is presented, and the measurement of various emission lines is discussed in detail. Important physical parameters are derived, including those pertaining to atomic data, line widths, physical conditions, geometry and kinematics, the Balmer decrement, and ultraviolet emission lines. The Seyfert characteristics of NGC 7213 are reviewed, and the galaxy's shock features are reconciled with photoionization models. The presented arguments may apply to classical liners as well. Theoretical models that can help explain the relationships discovered among the emission lines are examined.

Filippenko, A. V.↗