Convection, Thermal Bifurcation, and the Colors of A stars

Broad-band ultraviolet photometry from the TD-1 satellite and low dispersion spectra from the short wavelength camera of IUE have been used to investigate a long-standing proposal of Bohm-Vitense that the normal main sequence A- and early-F stars may divide into two different temperature sequences: (1) a high temperature branch (and plateau) comprised of slowly rotating convective stars, and (2) a low temperature branch populated by rapidly rotating radiative stars. We find no evidence from either dataset to support such a claim, or to confirm the existence of an "A-star gap" in the B-V color range 0.22 <= B-V <= 0.28 due to the sudden onset of convection. We do observe, nonetheless, a large scatter in the 1800--2000 A colors of the A-F stars, which amounts to ~0.65 mags at a given B-V color index. The scatter is not caused by interstellar or circumstellar reddening. A convincing case can also be made against binarity and intrinsic variability due to pulsations of delta Sct origin. We find no correlation with established chromospheric and coronal proxies of convection, and thus no demonstrable link to the possible onset of convection among the A-F stars. The scatter is not instrumental. Approximately 0.4 mags of the scatter is shown to arise from individual differences in surface gravity as well as a moderate spread (factor of ~3) in heavy metal abundance and UV line blanketing. A dispersion of ~0.25 mags remains, which has no clear and obvious explanation. The most likely cause, we believe, is a residual imprecision in our correction for the spread in metal abundances. However, the existing data do not rule out possible contributions from intrinsic stellar variability or from differential UV line blanketing effects owing to a dispersion in microturbulent velocity.Comment: 40 pages, 14 figures, 1 table, AAS LaTex, to appear in The Astrophysical Journa

Spectroscopic Determination of the Physical Conditions in Hot, Optically Thin Sources

This annual report covers the period from Oct 1, 2000 to Sep 30, 2001. The Astrophysics Plasma Emission Code and Database (APEC/APED), developed in part under this grant, have been upgraded to Version 1.1 and are now beginning to be used outside our research group in applications to X-ray spectral data from Chandra and XMM-Newton. These models represent the best theoretical data currently available and are reasonably complete below about 30 angstroms. Stellar coronae are being used to benchmark the atomic data in APED as part of the Emission Line Project. Initial results suggest that the models for most of the strongest lines are in good agreement with the observations, including the H-like and He-like emission from dominant elements and the Fe L shell emission, both near 1 keV and in the extreme ultraviolet near 100 eV. At this point in time, we define 'good agreement' at the level of accuracy expected from the atomic physics, approximately 20-30%. In order to benchmark the spectral models beyond the canonical theoretical accuracy, we are working closely with the Chandra gratings calibration group to ensure that we are using the optimal calibration, primarily effective areas and line response functions

Neutral Atomic Emissions From Comet Hale-Bopp

High resolution (R=100,000) spectra of atomic oxygen, hydrogen, and carbon from Comet Hale-Bopp were obtained at the NSO McMath-Pierce main telescope from February 8 to April 19, 1997, using a 50 mm dual-etalon Fabry-Perot/CCD spectrometer. The field of view was 6 arcmin. Spectra with good signal-to-noise were obtained for the emission lines [O I] 6300 Angstroms, Hα (6563 Angstroms), and [C I] 9850 Angstroms. On several of these nights, complementary [O I] 6300 Angstroms observations were simultaneously obtained with the Wisconsin Hα Mapper (WHα M) at Kitt Peak. Additional [O I] 6300 Angstroms observations were also obtained in September 1996. These [C I] 9850 Angstroms observations are the first extensive data set of this cometary line. We will present an overview of our observations and preliminary results

Lunar Sodium and Potassium Exosphere in May 2014

We apply high resolution spectroscopy to investigate the lunar exosphere by measuring sodium and potassium spectral line profiles to determine the variations in exospheric effective temperatures and velocities. Observations were made at the National Solar Observatory McMath-Pierce Telescope during May 2014. Data were collected over several nights, centered on full moon (May 14) and covering a waxing phase angle of 67 to a waning phase angle of 75. We used a dual-etalon Fabry-Perot spectrometer with a resolving power of 184,000 (1.63 km s-1) to measure the line widths and radial velocity shifts of the sodium D2 (5889.951 ) and potassium D1 (7698.965 ) emission lines. The field of view was 3 arcmin (~330 km) and positioned at several locations, each centered at 1.5 arcmin (~165 km) off the East and West sunlit limbs. The deconvolved line widths indicate significant differences between the sodium and potassium temperatures. The sodium line widths were mostly symmetric as a function of phase for both the waxing and waning phases. At phase angles \u3e 40 (outside of the magnetotail) the full width half maximum (FWHM) line widths are 1.5 2.0 km s-1 or ~1500 K for FWHM = 1.75 km s-1. Inside the magnetotail (phase angle \u3c 40) and near full moon (phase angle ~6), the FWHM increased to ~4 km s-1. The implied line width temperature is 8000 K, although some of the observed line width may be due to a dispersion in velocities from many contribution along the extended sodium tail. Unlike sodium, the potassium line widths are wider by 50% during the waxing phase compared to the waning phase at phases \u3e 40. The potassium temperatures pre-magnetotail passage are ~1000 K while the temperatures post-magnetotail passage are ~2000K.At phase angles \u3c 40, the potassium intensities decreased dramatically; on consecutive days, when the phase angle changed from 44 to 31 to 20, the relative intensities dropped by 1.0:0.6:0.15.The potassium intensity in the East and West equatorial regions (latitude \u3c 10) were similar; however, the potassium intensity was brightest off the limb near Aristarchus (latitude ~24), which was the crater we observed nearest the KREEP region

High-Spectral Resolution, May 2013 Ground-Based Observations of the Lunar Sodium and Potassium Exosphere

We apply high resolution spectroscopy to investigate the lunar exosphere by measuring sodium and potassium spectral line profiles to determine the variations in exospheric effective temperatures and velocities as a function of time, solar conditions and geometries. Observations are made with a dual-etalon Fabry-Perot spectrometer from the National Solar Observatory McMath-Pierce Telescope. The spectrometer has a Field of View (FOV) of 3 arcmin (~336 km at semimajor axis = 384,400 km) and a resolving power of 180,000 and 150,000 to measure the line widths and radial velocity Doppler shifts of the sodium D2 (5889.951 Å) and potassium D1 (7698.965 Å) emission lines, respectively. We first measured the sodium profile in March 2009 [1] followed by the first potassium line profile measurements in June 2012 (Fig. 1) during the moon’s waning gibbous phase. As previously reported [2], [3] potassium has a smaller scale height than sodium (Fig. 1). We only detected the potassium emission within ~0.25 Rmoon of the lunar limb while we measure sodium out to ~1 Rmoon. A lunar scattered light gradient underlying the FabryPerot circular interference fringes is the dominant continuum source and limiting factors in the precision of these measurements

High-Spectral Resolution, Ground-Based Observations of the Lunar Sodium and Potassium Exosphere During the LADEE Mission

We apply high resolution spectroscopy to investigate the lunar exosphere by measuring sodium and potassium spectral line profiles to determine the variations in exospheric effective temperatures and velocities. Observations were made at the National Solar Observatory McMath-Pierce Telescope concurrent with the Lunar Atmosphere and Dust Environment Explorer (LADEE) science phase. We used a dual-etalon Fabry-Perot spectrometer with a resolving power of 200,000 to measure the line widths and radial velocity Doppler shifts of the sodium D2 (5889.951 Å) and potassium D1 (7698.965 Å) emission lines. Data were taken during the full moon periods from November 2013 through May 2014 with the exception of March 2014. The instrument’s Field of View (FOV) of 3 arcmin (~360 km) was positioned at several locations, centered at 1.5 arcmin, off the East and West limbs. The deconvolved line widths indicate sodium temperatures pre- and post- magnetotail passage are on the order of 1600 K while temperatures during passage through the magnetotail are on the order of a several thousand Kelvin. Unlike sodium, the potassium deconvolved line widths indicate pre-magnetotail passage several hundred degrees hotter than the post-magnetotail passage temperatures. Additionally, both sodium and potassium intensities were brighter after magnetotail passage than before. This work was partially supported by the NASA Planetary Astronomy programs, NNX11AE38G and NNX13AL30G

High-Resolution Potassium Observations of the Lunar Exosphere

We observed lunar exospheric potassium D1 (7,698.9646 ) emissions using a high-spectral resolution Fabry-Perot spectrometer in 2014. We present the first potassium line profile measurements, which are representative of the potassium velocity distribution. Inferred temperatures are greater during the waxing gibbous phase, 1920 630 K and lower at waning gibbous phase, 980 200 K. Exosphere models suggest that the measured line widths are a combination of photon-stimulated desorption and impact vaporization sources. The relative potassium emission intensity decreases by 2.5 between lunar phases 80 and 30 and is brightest off the northwest limb near the Aristarchus crater, which is a potassium-rich surface region. Additionally, the emissions off the northern limb are brighter than the southern limb. The intensity decrease and the greater line width during the waxing gibbous versus the waning gibbous phase suggests a dawn-dusk asymmetry

High-Resolution, Ground-Based Observations of the Lunar Sodium Exosphere During the Lunar Atmosphere and Dust Environment Explorer (LADEE) Mission

Plain Language Summary We present the first comprehensive set of lunar exospheric line width and line width derived effective temperatures as a function of lunar phase (66 degrees waxing phase to 79 degrees waning phase). Data were collected between November 2013 and May 2014 during six observing runs at the National Solar Observatory McMath-Pierce Solar Telescope by applying high-resolution Fabry-Perot spectroscopy (R similar to 180,000) to observe emission from exospheric sodium (5,889.9509 angstrom, D2 line). The 3-arcmin field of view of the instrument, corresponding to similar to 336km at the mean lunar distance (384,400km), was positioned at several locations off the lunar limb; only equatorial observations taken out to 950km are presented here. We find the sodium effective temperature distribution to be approximately a symmetric function of lunar phase with respect to full Moon. Within magnetotail passage we find temperatures in the range of 2500-9000K. For phase angles greater than 40 degrees we find that temperatures flatten out to similar to 1700K. High spectral resolution observations of optical line emissions are used to investigate the morphology and dynamics of the lunar sodium exosphere. These observations were obtained from the National Solar Observatory McMath-Pierce Solar Telescope, coincident with the Lunar Atmosphere and Dust Environment Explorer mission. The equatorial data presented here are the first comprehensive set of direct sodium emission line profile observations of the lunar exosphere. These observations will help constrain atmospheric and surface process modeling, and help quantify lunar exospheric source and escape mechanisms. Studying the morphology of the lunar exosphere with altitude and local time provides a useful laboratory for testing space weather effects at Earth and theoretical models of other bodies with similar exospheres (e.g., Mercury).NASA [NNX11AE38G, NNX13AL30G]; Solar System Exploration Research Virtual Institute (SSERVI)6 month embargo; published online: 25 August 2018This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

The Wisconsin/GSFC Hale-Bopp Observing Campaign

From September 1996 to April 1997, we conducted an extensive campaign of observations of several atomic (O, C, H), ionic (H_2O(+) ), and molecular (OH, C_2, C_3, CN, NH_2) emissions from Comet Hale-Bopp, using a variety of telescopes (McMath-Pierce, WHAM, Burrel-Schmidt, WIYN, PBO, WISP), instruments (imagers, Fabry-Perot and grating spectrometers, polarimeters), and data formats (spectra, images, datacubes). We will present an overview of the observations, and highlight early results, some of which will be presented in detail in poster papers at this meeting