Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “stellar photometry”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS2023

TOI-5344 b: A Saturn-like Planet Orbiting a Super-solar Metallicity M0 Dwarf

We confirm the planetary nature of TOI-5344 b as a transiting giant exoplanet around an M0-dwarf star. TOI-5344 b was discovered with the Transiting Exoplanet Survey Satellite photometry and confirmed with ground-based photometry (the Red Buttes Observatory 0.6 m telescope), radial velocity (the Habitable-zone Planet Finder), and speckle imaging (the NN-Explore Exoplanet Stellar Speckle Imager). TOI-5344 b is a Saturn-like giant planet (ρ = 0.80 +0.17 −0.15 g cm −3 ) with a planetary radius of 9.7 ± 0.5 R⊕ (0.87 ± 0.04 R Jup ) and a planetary mass of 135 +17 −18 M⊕ (0.42 +0.05 −0.06 M Jup ). It has an orbital period of 3.792622 +0.000010 −0.000010 days and an orbital eccentricity of 0.06 +0.07 −0.04 . We measure a high metallicity for TOI-5344 of [Fe/H] = 0.48 ± 0.12, where the high metallicity is consistent with expectations from formation through core accretion. We compare the metallicity of the M-dwarf hosts of giant exoplanets to that of M-dwarf hosts of nongiants (≲8 R⊕). While the two populations appear to show different metallicity distributions, quantitative tests are prohibited by various sample caveats.

Te Han↗
NASA NTRS1985

Images in the rocket ultraviolet - The initial helium abundance and distance modulus of the globular cluster M5 from photometry of horizontal-branch stars

A natural laboratory for the study of postmain-sequence evolution of low-mass (less than one solar mass) metal-poor stars is provided by globular clusters. These clusters are, therefore, a critical aid for developing an understanding of advanced stages of stellar evolution and of the chemical evolution of the Galaxy. Bohlin et al. (1983) have described a study of the postasymptotic branch star near the center of M5. The present investigation is concerned with the fainter horizontal-branch stars. The observations were made with the aid of a rocket-borne 38 cm f/9.0 Ritchey-Chretien telescope. Attention is given to payload and flight data, preflight bandpass calibration, the reduction of flight data, star selection, position measurement, photometry, the minimum observed horizontal-branch mass and inferences on mass loss, and individual UV-bright stars.

Bohlin, R. C.↗
NASA NTRS1973

UV photometry of eclipsing variables

UV photometric observations of the eclipsing variable CW Cephei by orbiting OAO-2 instrument package reveal the binary to be a system in an active stage of evolution, with evidence for stellar mass loss or mass exchange.

Sobieski, S.↗
NASA NTRS2013

Uv-bright Nearby Early-type Galaxies Observed in the Mid-infrared: Eidence for a Multi-stage Formation History by Way of WISE and GALEX Imaging

In the local universe, 10% of massive elliptical galaxies are observed to exhibit a peculiar property: a substantial excess of ultraviolet emission than what is expected from their old, red stellar populations. Several origins for this ultraviolet excess (UVX) have been proposed including a population of hot young stars and a population of old, blue horizontal branch or extended horizontal branch (BHB or EHB) stars that have undergone substantial mass loss from their outer atmospheres. We explore the radial distribution of UVX in a selection of 49 nearby E/S0-type galaxies by measuring their extended photometry in the UV through mid-infrared (mid-IR) with the Galaxy Evolution Explorer (GALEX), the Sloan Digital Sky Survey, and the Wide-field Infrared Survey Explorer (WISE). We compare UV/optical and UV/mid-IR colors with the Flexible Stellar Population Synthesis models, which allow for the inclusion of EHB stars. We find that combined WISE mid-IR and GALEX UV colors are more effective in distinguishing models than optical colors, and that the UV/mid-IR combination is sensitive to the EHB fraction. There are strong color gradients, with the outer radii bluer than the inner half-light radii by approx.1 mag. This color difference is easily accounted for with an increase in the BHB fraction of 0.25 with radius. We estimated that the average ages for the inner and outer radii are 7.0 +/- 0.3 Gyr, and 6.2 +/- 0.2 Gyr, respectively, with the implication that the outer regions are likely to have formed approx. 1 Gyr after the inner regions. Additionally, we find that metallicity gradients are likely not a significant factor in the color difference. The separation of color between the inner and outer regions, which agrees with a specific stellar population difference (e.g., higher EHB populations), and the approx. 0.5-2 Gyr age difference suggests multi-stage formation. Our results are best explained by inside-out formation: rapid star formation within the core at early epochs (>4 Gyr ago) and at least one later stage starburst event coinciding with z approx. 1.

galaxies: elliptical and lenticular↗
DOE OSTI2022

J-PLUS: Uncovering a large population of extreme [OIII] emitters in the local Universe

Over the past decades, several studies have discovered a population of galaxies that undergo very strong star formation events. They are called extreme emission line galaxies (EELGs). We exploit the capabilities of the Javalambre Photometric Local Universe Survey (J-PLUS), a wide-field multifilter survey, with which 2000 square degrees of the northern sky are already observed. We use it to identify EELGs at low redshift by their [OIII]5007 emission line. We intend to provide a more complete, deep, and less biased sample of local EELGs. We selected objects with an excess of flux in the J-PLUS medium-band J0515 filter, which covers the [OIII] line at z < 0.06. We removed contaminants (stars and higher-redshift systems) using J-PLUS and WISE infrared photometry, with SDSS spectra as a benchmark. We performed spectral energy distribution fitting to estimate the physical properties of the galaxies: line fluxes, equivalent widths (EWs), masses, stellar population ages, and so on. We identify 466 EELGs at z < 0.06 with [OIII] EW over 300 Å and an r-band magnitude below 20, of which 411 were previously unknown. Most show compact morphologies, low stellar masses (log(M • /M ⊙ ) ~ 8.13 –0.58 +0.61 ), low dust extinction (E( B–V ) ~ 0.1 –0.1 +0.2 ), and very young bursts of star formation (3.0 –2.0 +2.7 Myr). Our method is up to ~20 times more efficient in detecting EELGs per Mpc 3 than broadband surveys, and it is as complete as magnitude-limited spectroscopic surveys (but reaches fainter objects). The sample is not directly biased against strong Hα emitters, in contrast with works using broadband surveys. We demonstrate that J-PLUS can identify a large sample of previously unknown EELGs showing unique properties following a clear selection process. A fraction of the EELGs are probably similar to the first galaxies in the Universe, but they are at a much lower redshift, which makes them ideal targets for follow-up studies.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1984

Photometric Variations of Solar-type Stars: Results of the Cloudcroft Survey

The results of a synoptic program to search for the occurrence of photometric variability in solar type stars as seen in continuum band photometry are summarized. The survey disclosed the existence of photometric variability in solar type stars that is related to the presence of spots on the stellar surface. The observed variability detected in solar type stars is at enhanced levels compared to that observed for the Sun.

Giampapa, M. S.↗
NASA NTRS2013

The IMACS Cluster Building Survey. I. Description of the Survey and Analysis Methods

The IMACS Cluster Building Survey uses the wide field spectroscopic capabilities of the IMACS spectrograph on the 6.5 m Baade Telescope to survey the large-scale environment surrounding rich intermediate-redshift clusters of galaxies. The goal is to understand the processes which may be transforming star-forming field galaxies into quiescent cluster members as groups and individual galaxies fall into the cluster from the surrounding supercluster. This first paper describes the survey: the data taking and reduction methods. We provide new calibrations of star formation rates (SFRs) derived from optical and infrared spectroscopy and photometry. We demonstrate that there is a tight relation between the observed SFR per unit B luminosity, and the ratio of the extinctions of the stellar continuum and the optical emission lines.With this, we can obtain accurate extinction-corrected colors of galaxies. Using these colors as well as other spectral measures, we determine new criteria for the existence of ongoing and recent starbursts in galaxies.

IMACS↗
NASA NTRS1977

The University of Texas catalog of ultraviolet and optical stellar data

The paper describes a plan to assemble a master catalog of early-type stars to at least 10th magnitude, containing a single value for each magnitude and the spectral type, with information on photometry, known peculiarities, duplicity, etc., which will serve as a collection of ground-based data to aid in the reduction and analysis of ultraviolet spectra obtained with the S-019 experiment on Skylab, in which objective prism photographs recorded nearly 10,000 stars at wavelengths shortward of 3000 A. The starting point is the Celescope Identification Catalog; several other catalogs will be compared and merged with this data base. The format for recording the wanted data on magnetic tape and the procedure for assembling the master file are discussed.

Parsons, S. B.↗
NASA NTRS2004

Meteor44 Video Meteor Photometry

Meteor44 is a software system developed at MSFC for the calibration and analysis of video meteor data. The dynamic range of the (8bit) video data is extended by approximately 4 magnitudes for both meteors and stellar images using saturation compensation. Camera and lens specific saturation compensation coefficients are derived from artificial variable star laboratory measurements. Saturation compensation significantly increases the number of meteors with measured intensity and improves the estimation of meteoroid mass distribution. Astrometry is automated to determine each image s plate coefficient using appropriate star catalogs. The images are simultaneously intensity calibrated from the contained stars to determine the photon sensitivity and the saturation level referenced above the atmosphere. The camera s spectral response is used to compensate for stellar color index and typical meteor spectra in order to report meteor light curves in traditional visual magnitude units. Recent efforts include improved camera calibration procedures, long focal length "streak" meteor photome&y and two-station track determination. Meteor44 has been used to analyze data from the 2001.2002 and 2003 MSFC Leonid observational campaigns as well as several lesser showers. The software is interactive and can be demonstrated using data from recent Leonid campaigns.

Swift, Wesley R.↗
DOE OSTI2021

Stellar Rotation of T Tauri Stars in the Orion Star-forming Complex

We present a large-scale study of stellar rotation for T Tauri stars in the Orion star-forming complex. We use the projected rotational velocity ($v\sin (i)$) estimations reported by the APOGEE-2 collaboration as well as individual masses and ages derived from the position of the stars in the HR diagram, considering Gaia-EDR3 parallaxes and photometry plus diverse evolutionary models. We find an empirical trend for $v\sin (i)$ decreasing with age for low-mass stars (0.4M ⊙ < M $\star$ < 1.2M ⊙ ). Our results support the existence of a mechanism linking $v\sin (i)$ to the presence of accreting protoplanetary disks, responsible for regulating stellar rotation on timescales of about 6 Myr, which is the timescale in which most of the T Tauri stars lose their inner disk. Our results provide important constraints to models of rotation in the early phases of evolution of young stars and their disks.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

APOGEE Net: Improving the Derived Spectral Parameters for Young Stars through Deep Learning

Machine learning allows for efficient extraction of physical properties from stellar spectra that have been obtained by large surveys. The viability of machine-learning approaches has been demonstrated for spectra covering a variety of wavelengths and spectral resolutions, but most often for main-sequence (MS) or evolved stars, where reliable synthetic spectra provide labels and data for training. Spectral models of young stellar objects (YSOs) and low-mass MS stars are less well-matched to their empirical counterparts, however, posing barriers to previous approaches to classify spectra of such stars. In this work, we generate labels for YSOs and low-mass MS stars through their photometry. We then use these labels to train a deep convolutional neural network to predict logg, T {sub eff}, and Fe/H for stars with Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra in the DR14 data set. This “APOGEE Net” has produced reliable predictions of logg for YSOs, with uncertainties of within 0.1 dex and a good agreement with the structure indicated by pre-MS evolutionary tracks, and it correlates well with independently derived stellar radii. These values will be useful for studying pre-MS stellar populations to accurately diagnose membership and ages.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Close Major-merger Pairs at z = 0: Star-forming Galaxies with Pseudobulges

Abstract We present a study of star-forming galaxies (SFGs) with pseudobulges (bulges with Sérsic indexn< 2) in a local close major-merger galaxy pair sample (H-KPAIR). With data from new aperture photometries in the optical and near-infrared bands (aperture size of 7 kpc) and from the literature, we find that the mean Age of central stellar populations in Spirals with pseudobulges is consistent with that of disky galaxies and is nearly constant against the bulge-to-total ratio (B/T). Paired Spirals have a slightly lower fraction of pure disk galaxies (B/T ≤ 0.1) than their counterparts in the control sample. Compared to SFGs with classical bulges, those with pseudobulges have a higher (>2σ) mean of specific star formation rate (sSFR) enhancement (sSFR enh = 0.33 ± 0.07 versus sSFR enh = 0.12 ± 0.06) and broader scatter (by ∼1 dex). The eight SFGs that have the highest sSFR enh in the sample all have pseudobulges. A majority (69%) of paired SFGs with strong enhancement (having sSFR more than 5 times the median of the control galaxies) have pseudobulges. The Spitzer data show that the pseudobulges in these galaxies are tightly linked to nuclear/circum-nuclear starbursts. Pseudobulge SFGs in S+S and in S+E pairs have significantly (>3σ) different sSFR enhancement, with the means of sSFR enh = 0.45 ± 0.08 and −0.04 ± 0.11, respectively. We find a decrease in the sSFR enhancements with the density of the environment for SFGs with pseudobulges. Since a high fraction (5/11) of pseudobulge SFGs in S+E pairs are in rich groups/clusters (local density N 1Mpc ≥ 7), the dense environment might be the cause for their low sSFR enh .

Astronomy & Astrophysics↗
DOE OSTI2021

A panoramic view of the Local Group dwarf galaxy NGC 6822

ABSTRACT We present a panoramic survey of the isolated Local Group dwarf irregular galaxy NGC 6822. Our photometry reaches ∼2–3 mag deeper than most previous studies and spans the widest area around the dwarf compared to any prior work. We observe no stellar overdensities in the outskirts of NGC 6822 to V ∼ 30 mag arcsec−2 and a projected radius of 16.5 kpc. This indicates that NGC 6822 has not experienced any recent interaction with a companion galaxy, despite previous suggestions to the contrary. Similarly, we find no evidence for any dwarf satellites of NGC 6822 to a limiting luminosity MV ≈ −5. NGC 6822 contains a disc of H i gas and young stars, oriented at ∼60○ to an extended spheroid composed of old stellar populations. We observe no correlation between the distribution of young stars and spheroid members. Our imaging allows us to trace the spheroid to nearly 11 kpc along its major axis, commensurate with the extent of the NGC 6822 globular cluster system. We find that the spheroid becomes increasingly flattened at larger radii, and its position angle twists by up to 40○. We use Gaia EDR3 astrometry to measure a proper motion for NGC 6822, and then sample its orbital parameter space. While this galaxy has spent the majority of its life in isolation, we find that it likely passed within the virial radius of the Milky Way ∼3–4 Gyr ago. This may explain the apparent flattening and twisting observed in the outskirts of its spheroid.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1978

The light curve of the nucleus of comet d'Arrest

This paper reports new photoelectric photometry of the nucleus of P/d'Arrest (1976e) during August 4, 5, and 6, 1976 (UT), just before perihelion passage. The comet appeared as a bright stellar nucleus with a faint surrounding coma. The average visual magnitude from the nuclear region (16-arcsec diaphragm) was 11.60. The visual brightness varies with an amplitude of 0.15 plus or minus 0.02 mag. There is evidence for a period of 5.17 plus or minus 0.01 hr. We interpret such a periodic variation as due to the rotation of the nucleus. The colors of the nuclear region are very similar to those of a solar-type star, and they do not vary significantly with aspect angle.

Fay, T. D., Jr.↗
NASA NTRS1984

An infrared disk at the center of the bipolar planetary nebula NGC 6302

Broad-band infrared photometry and high-resolution infrared maps are presented for NGC 6302, a bipolar planetary nebula in which material is being driven outward by a powerful stellar wind. The infrared morphology is very unlike that seen optically. Maps at 1.25, 2.2, 3.4, and 10 microns show evidence for a disk of material with its short axis oriented parallel to the supersonic flow and located between the optical lobes. This structure is not optically evident partly because of the large extinction along the line of sight to the nebular core. It is suggested that the observed disk is either an expanded fossil toroid that once confined the flow, or else is stellar envelope material that was not in the path of the bipolar flow and that remains in the vicinity of the stellar remnant.

Lester, D. F.↗
NASA NTRS1995

The fate of the solid matter orbiting HR 4796A

We have obtained optical spectra, 2 micrometers speckle images, and an upper limit to the 800 micrometers flux for HR 4796A, and optical spectra for its physical companion separated by 7.7 arcsecs, HR 4796B. We detect H-beta, H-gamma, and the calcium H and K lines in emission from HR 4796B; these data are consistent with the hypothesis that it is later than spectral type M2 and lies substantially above the main-sequence. From the location of HR 4796B on the H-R diagram, the estimated age of this star is 3 x 10(exp 6) yr, and assuming this age for the entire system, we find from our 2 micrometers speckle data that there is no close stellar companion to HR 4796A (M greater than 0.125 solar mass) between 11 and 120 AU from the star. From the IRAS and ground-based photometry, it seems that there is a hole in the dust distribution around HR 4796A with an inner radius of between approximately 40 and approximately 200 AU. The observed circumstellar dust grains, which lie at D greater than 40 AU from the star, are likely to be at least 3 micrometers in radius in order to be gravitationally bound to HR 4796A, if the circumstellar dust cloud is optically thin. Since they are larger than almost all interstellar grains, the circumstellar dust grains probably grew by coalescence. Because the existing grains at D greater than 40 AU have undergone measurable coalescence, it is possible that particles that presumably once existed at D less than 40 AU, where the collision times were shorter than at D greater than 40 AU, grew into macroscopic objects. A likely explanation for the dust hole is that there is a companion located at about half the inner radius of the dust hole, or between 20 and 100 AU from the star. If such a companion exists, it must have a mass less than 0.125 solar mass. Since grain coalescence has occurred, this putative companion possibly could be a planet.

Jura, M.↗
NASA NTRS1972

Ultraviolet photometry of planetary nebulae

Nine of the planetary nebulae observed by the Wisconsin filter photometers are compared with 15 Monocerotis in the spectral region 1430-4250 A. The data are corrected for the degradation of the filters of stellar photometer number four with time. Comparisons with simple models indicate that most of the observed nebulae are subject to some interstellar extinction in the far ultraviolet. However, NGC 246 and NGC 1360 appear to be nearly unreddened. Thus far no unexpected features have been found in the observations.

Holm, A. V.↗
DOE OSTI2024

Red supergiant candidates for multimessenger monitoring of the next Galactic supernova

ABSTRACT We compile a catalogue of 578 highly probable and 62 likely red supergiants (RSGs) of the Milky Way, which represents the largest list of Galactic RSG candidates designed for continuous follow-up efforts to date. We match distances measured by Gaia DR3, 2MASS photometry, and a 3D Galactic dust map to obtain luminous bright late-type stars. Determining the stars’ bolometric luminosities and effective temperatures, we compare to Geneva stellar evolution tracks to determine likely RSG candidates, and quantify contamination using a catalogue of Galactic AGB in the same luminosity-temperature space. We add details for common or interesting characteristics of RSG, such as multistar system membership, variability, and classification as a runaway. As potential future core-collapse supernova progenitors, we study the ability of the catalogue to inform the Supernova Early Warning System (SNEWS) coincidence network made to automate pointing, and show that for 3D position estimates made possible by neutrinos, the number of progenitor candidates can be significantly reduced, improving our ability to observe the progenitor pre-explosion and the early phases of core-collapse supernovae.

Astronomy & Astrophysics↗