Engineering topics

Drake, Jeremy J.

Publications and source records attributed to Drake, Jeremy J..

14 records

DOE OSTI2022

The Factory and the Beehive. IV. A Comprehensive Study of the Rotation X-Ray Activity Relation in Praesepe and the Hyades

X-ray observations of low-mass stars in open clusters are critical to understanding the dependence of magnetic activity on stellar properties and their evolution. Praesepe and the Hyades, two of the nearest, most-studied open clusters, are among the best available laboratories for examining the dependence of magnetic activity on rotation for stars with masses ≲1 M ⊙ . We present an updated study of the rotation–X-ray activity relation in the two clusters. We updated membership catalogs that combine pre-Gaia catalogs with new catalogs based on Gaia Data Release 2. The resulting catalogs are the most inclusive ones for both clusters: 1739 Praesepe and 1315 Hyades stars. We collected X-ray detections for cluster members, for which we analyzed, re-analyzed, or collated data from ROSAT, the Chandra X-ray Observatory, the Neil Gehrels Swift Observatory, and XMM-Newton. We have detections for 326 Praesepe and 462 Hyades members, of which 273 and 164, respectively, have rotation periods—an increase of 6× relative to what was previously available. We find that at ≈700 Myr, only M dwarfs remain saturated in X-rays, with only tentative evidence for supersaturation. We also find a tight relation between the Rossby number and fractional X-ray luminosity L X /L bol in unsaturated single members, suggesting a power-law index between –3.2 and –3.9. Lastly, we find no difference in the coronal parameters between binary and single members. These results provide essential insight into the relative efficiency of magnetic heating of the stars' atmospheres, thereby informing the development of robust age-rotation-activity relations.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2022

New Clues to the Evolution of Dwarf Carbon Stars From Their Variability and X-Ray Emission

As main-sequence stars with C > O, dwarf carbon (dC) stars are never born alone but inherit carbon-enriched material from a former asymptotic giant branch (AGB) companion. In contrast to M dwarfs in post-mass-transfer binaries, C 2 and/or CN molecular bands allow dCs to be identified with modest-resolution optical spectroscopy, even after the AGB remnant has cooled beyond detectability. Accretion of substantial material from the AGB stars should spin up the dCs, potentially causing a rejuvenation of activity detectable in X-rays. Indeed, a few dozen dCs have recently been found to have photometric variability with periods under a day. However, most of those are likely post-common-envelope binaries, spin–orbit locked by tidal forces, rather than solely spun-up by accretion. Here, we study the X-ray properties of a sample of the five nearest-known dCs with Chandra. Two are detected in X-rays, the only two for which we also detected short-period photometric variability. We suggest that the coronal activity detected so far in dCs is attributable to rapid rotation due to tidal locking in short binary orbits after a common-envelope phase, late in the thermally pulsing (TP) phase of the former C-AGB primary (TP-AGB).

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

X-Rays in Cepheids: XMM-Newton Observations of η Aql

X-ray bursts have recently been discovered in the Cepheids δ Cep and β Dor modulated by the pulsation cycle. We have obtained an observation of the Cepheid η Aql with the XMM-Newton satellite at the phase of maximum radius; the phase at which there is a burst of X-rays in δ Cep. No X-rays were seen from the Cepheid η Aql at this phase, and the implications for Cepheid upper atmospheres are discussed. We have also used the combination of X-ray sources, as well as Gaia and 2MASS data, to search for a possible grouping around the young intermediate mass Cepheid. No indication of such a group was found.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2020

The High-energy Radiation Environment around a 10 Gyr M Dwarf: Habitable at Last?

Recent work has demonstrated that high levels of X-ray and UV activity on young M dwarfs may drive rapid atmospheric escape on temperate, terrestrial planets orbiting within the habitable zone. However, secondary atmospheres on planets orbiting older, less active M dwarfs may be stable and present more promising candidates for biomarker searches. In order to evaluate the potential habitability of Earth-like planets around old, inactive M dwarfs, we present new Hubble Space Telescope and Chandra X-ray Observatory observations of Barnard’s Star (GJ 699), a 10 Gyr old M3.5 dwarf, acquired as part of the Mega-MUSCLES program. Despite the old age and long rotation period of Barnard’s Star, we observe two FUV (δ 130 ≈ 5000 s; E 130 ≈ 10 29.5 erg each) and one X-ray (E X ≈ 10 29.2 erg) flares, and we estimate a high-energy flare duty cycle (defined here as the fraction of the time the star is in a flare state) of ~25%. A publicly available 5 Å to 10 μm spectral energy distribution of GJ 699 is created and used to evaluate the atmospheric stability of a hypothetical, unmagnetized terrestrial planet in the habitable zone (r HZ ~ 0.1 au). Both thermal and nonthermal escape modeling indicate (1) the quiescent stellar XUV flux does not lead to strong atmospheric escape: atmospheric heating rates are comparable to periods of high solar activity on modern Earth, and (2) the flare environment could drive the atmosphere into a hydrodynamic loss regime at the observed flare duty cycle: sustained exposure to the flare environment of GJ 699 results in the loss of ≈87 Earth atmospheres Gyr -1 through thermal processes and ≈3 Earth atmospheres Gyr -1 through ion loss processes. These results suggest that if rocky planet atmospheres can survive the initial ~5 Gyr of high stellar activity, or if a second-generation atmosphere can be formed or acquired, the flare duty cycle may be the controlling stellar parameter for the stability of Earth-like atmospheres around old M stars.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2004

The Herbig Ae Star HD 163296 in X-Rays

Chandra X-ray imaging spectroscopy of the nearby Herbig Ae star HD 163296 at 100 AU angular resolution is reported. A point-like, soft (kT approximately 0.5 approximately kev), emission-line source is detected at the location of the star with an X-ray luminosity of 4.0e29 erg/s. In addition, faint emission along the direction of a previously-detected Ly-alpha-emitting jet and Herbig-Haro outflow may be present. The relatively low luminosity, lack of a hard spectral component, and absence of strong X-ray variability in HD 163296 can be explained as originating from optically-thin shock-heated gas accreting onto the stellar surface along magnetic field lines. This would require a (dipole) magnetic field strength at the surface of HD 163296 of at least approximately 100 approximately G and perhaps as high as several kG.

Swartz, Douglas A.↗

NASA NTRS2000

In Pursuit of the FIP Effect in Stellar Coronae

Observational data have been reduced. Sig Gem data have been fitted using the XSPEC software, though the treatment within this software of the Fe transitions arising from the n=2 levels is thought to be sufficiently inaccurate as to affect the results obtained. Data for the same star obtained by EUVE have been extracted from the archive and are being analyzed in order to try and constrain the coronal DEM. Results of the first sets of model fitting have been presented at an AAS meeting; a more substantial presentation of these and updated results in a main-stream referred journal is in progress.

Drake, Jeremy J.↗

NASA NTRS1999

Coronally Fluoresced Stellar Photospheric X-Ray Spectra

Monte Carlo computations of photospheric fluorescent x-ray spectra are described. X-rays emitted from a hot corona incident on an underlying photosphere can undergo either scattering events by Compton scattering or photoabsorption events through the ionization of atoms or weakly ionized species. Through scattering events, photons can be reflected back in a direction towards the stellar surface where they have a finite chance of escape. Photoionization events involving x-ray photons directed toward the photosphere are predominantly inner shell interactions, Observable fluorescent lines can arise as a result of the finite escape probabilities of photons emitted in outward directions by hole transitions in these atoms. For a given stellar composition, fluorescent line strengths are dependent on the height of the fluorescing source above the photosphere and on the angle between the source and the observer. Although the only fluorescent lines likely to be detected in stellar coronae are Fe Ka and perhaps O Ka, these lines could provide powerful and direct spectroscopic diagnostics of coronal geometry.

Drake, Jeremy J.↗

NASA NTRS1999

On Photospheric Fluorescence and the Nature of the 17.62 Angstrom Feature in Solar X-ray Spectra

The identification of the emission line feature at 17.62 Angstroms in solar x-ray spectra is re-examined. Using a Monte Carlo technique, we compute a realistic theoretical upper limit to the observed Fe L-alpha photospheric fluorescent line strength caused by irradiation from an overlying corona. These calculations demonstrate that the photospheric Fe L-alpha characteristic line is much too weak to account for the observed 17.62 Angstrom line flux. Instead, we identify this line with the configuration interaction 2s2p3p2P-2s2p6 2S transition in Fe XVIII seen in Electron Beam Ion Trap spectra and predicted in earlier theoretical work on the Fe XVIII x-ray spectrum.

Drake, Jeremy J.↗

NASA NTRS1995

A volume-limited survey of High Galactic latitude planetary nebulae with the Extrme Ultraviolet Explorer

We present the results of a complete survey, at extreme-ultraviolet (EUV) wavelengths (58-234 A), of the high Galactic latitude (absolute value of b greater than or = to 20 deg) planetary nebulae (PNs) with at least one determination of the distance within 1 kpc of the Sun. The sample comprises 27 objects observed during the Extreme Ultraviolet Explorer (EUVE) all-sky survey and represents the majority of PN likely to be accessible at EUV wavelengths. Six PNs (NGC 246, NGC 1360, K1-16, LoTr 5, NGC 4361, and NGC 3587) were detected in the shortest EUV band (58-174 A). A seventh PN (NGC 6853), not included in the sample, was also detected during the survey. The emission is consistent in all cases with that of a point source and therefore most probably originates from the PN central star. Accurate EUV count rates or upper limits in the two shorter EUVE bands (centered at approximately 100 and 200 A) are given for all the sources in the sample. NGC 4361 and NGC 3587 are reported here for the first time as sources of EUV radiation. As might be expected, attenuation by the interstellar medium dominates the PN distribution in the EUV sky.

Fruscione, Antonella↗

NASA NTRS1994

Sodium in weak G-band giants

Sodium abundances have been determined for eight weak G-band giants whose atmospheres are greatly enriched with products of the CN-cycling H-burning reactions. Systematic errors are minimized by comparing the weak G-band giants to a sample of similar but normal giants. If, further, Ca is selected as a reference element, model atmosphere-related errors should largely be removed. For the weak-G-band stars (Na/Ca) = 0.16 +/- 0.01, which is just possibly greater than the result (Na/Ca) = 0.10 /- 0.03 from the normal giants. This result demonstrates that the atmospheres of the weak G-band giants are not seriously contaminated with products of ON cycling.

Drake, Jeremy J.↗

NASA NTRS1994

Detection of rotational modulation in the coronal extreme-ultraviolet emission from V711 Tauri?

The RS CVn binary V711 Tauri was observed by the Extreme Ultraviolet Explorer satellite (EUVE) twice during the latter half of 1992, for periods lasting several days. Light curves for the waveband 60-180 A derived from the all-sky survey scanning in August and from a pointed calibration observation made in October both exhibit a modulation of about 40%. The modulation in both data sets is very similar, with minimum flux occurring near orbital phase phi = 0.5. Analysis using a two-temperature optically thin plasma emission model reveals that most of the detected extreme ultraviolet (EUV) flux emanates from hot (approximately 10(exp 7) K) coronal plasma. The modulation is probably mostly due to either flare-like activity or to rotational occultation of a long-lived, compact, and especially bright coronal structure on the more active star of the system. The phased data support the latter hypothesis. This coronal structure is then likely to be associated with the presistent spot patterns seen on V711 Tau when using Doppler and photometric surface imaging techniques. Comparison with contemporaneous Stroemgren b-band photometry indicates that the optical minimum light leads the EUV maximum light by 90 deg in phase.

Drake, Jeremy J.↗

NASA NTRS1993

Abundance inhomogeneities and atmospheric structure in CN-bimodal globular cluster giants

It has been suggested by several authors that the sodium and aluminum abundance variations correlating with CN-band strength, frequently observed in CN-bimodal globular cluster giants, could be spurious manifestations of different temperature structures in the 'CN-strong' and 'CN-weak' stars, caused by different molecular line blanketing related to the C, N, and O trio. For stellar parameters generally appropriate to giants in the intermediate metallicity CN-bimodal cluster M4, we demonstrate through new model atmosphere calculations, employing opacity sampling and spherical geometry, that the observed abundance anomalies cannot be the result of atmospheric temperature structure. Our results using spherical geometry are compared to identical calculations performed with plane-parallel geometry: the effects of atmospheric extension on derived abundances for all lines considered amount to less than 0.1 dex.

Drake, Jeremy J.↗

NASA NTRS1993

The fundamental parameters of the chromospherically active K2 dwarf Epsilon Eridani

A silicon array detector was used to record regions exhibiting calcium and iron lines in the spectrum of the chromospherically active K2 dwarf Epsilon Eri at a resolution of 120,000 and with an SNR of not less than 200. The effective temperature, surface gravity, logarithmic iron and calcium abundances, and microturbulence are determined. Three high-excitation lines of Fe I were found to yield anomalously low iron abundances; it is postulated that the origin of the anomaly lies in the nonthermal excitation of the upper photosphere caused by chromospheric emission. It is shown that Epsilon Eri is in an evolutionary stage consistent with an M/solar mass of 0.85 theoretical zero-age main-sequence model. It is suggested that Epsilon Eri is almost certainly a young star of slightly less than one solar mass.

Drake, Jeremy J.↗

NASA NTRS1992

The extreme ultraviolet explorer archive

The Extreme Ultraviolet Explorer (EUVE) satellite was launched successfully at 12:400:00 EDT on June 7, 1992 from Cape Canaveral Air Force Station, Florida. The EUVE science payload consists of three scanning telescopes carrying out an all-sky survey in the 70-760A spectral region, and a Deep Survey/Spectrometer telescope performing a deep survey in the 70-250A spectral region. This latter instrumentation will subsequently perform Guests Observer (GO) spectroscopic observations of individual targets. The EUVE public archive opened for business on July 17, 1992. The purpose of the archive is the storage and distribution of EUVE data and ancillary documentation, information and software which is in the public domain. As the mission proceeds, the all-sky survey, deep survey and spectroscopic data will become publicly available through a variety of interfaces to an archive system centered around an optical juke box. In this paper, we describe the current and future contents, the architecture, and the development plans for the archive.

Drake, Jeremy J.↗