Stars, Interstellar Medium and the Galaxy Commons^™

The Expansion Center And Dynamical Age Of The Galactic Supernova Remnant Cassiopeia A, John R. Thorstensen, Robert A. Fesen, Sidney Van Den Bergh

Dartmouth Scholarship

We present proper motions for 21 bright main shell and 17 faint, higher velocity, outer ejecta knots in the Cas A supernova remnant and use them to derive new estimates for the remnant's expansion center and age. Our study included 1951–1976 Palomar 5 m prime focus plates, 1988–1999 CCD images from the KPNO 4 m and MDM 2.4 m telescopes, and 1999 HST WFPC2 images. Measurable positions covered a 23 to 41 yr time span for most knots, with a few outer knots followed for almost 48 yr. We derive an expansion center of α(J2000) = 23^h23^{m …}

A Search For Previously Unrecognized Metal-Poor Subdwarfs In The Hipparcos Astrometric Catalogue, I. N. Reid, F. Van Wyk, F. Marang, G. Roberts, D. Kilkenny, S. Mahoney

Dartmouth Scholarship

We have identified 317 stars included in the Hipparcos astrometric catalogue that have parallaxes measured to a precision of better than 15 per cent, and the location of which in the (M_V,(B−V)_T) diagram implies a metallicity comparable to or less than that of the intermediate‐abundance globular cluster M5. We have undertaken an extensive literature search to locate Strömgren, Johnson/Cousins and Walraven photometry for over 120 stars. In addition, we present new UBV(RI)_C photometry of 201 of these candidate halo stars, together with similar data for a further 14 known metal‐poor subdwarfs. These …

Infrared Spectroscopy Of Symbiotic Stars. Iii. First Orbits For Three S-Type Systems, Francis C. Fekel, Kenneth H. Hinkle, Richard Joyce, Michael F. Skrutskie

Information Systems and Engineering Management Research Publications

Infrared radial velocities have been used to derive the first well-determined orbital elements for the cool giants of three symbiotic systems, BF Cyg, V1329 Cyg, and V343 Ser=AS 289. Periods found for BF Cyg and V1329 Cyg from the radial velocity data are in good agreement with periods previously determined for their light variations, and the orbits are circular. Masses for the components of BF Cyg and V1329 Cyg were determined by combining our orbital elements for the cool giants with elements for their hot stars. BF Cyg and V1329 Cyg are shown to be detached binary systems. The third …

0920+3517_Nir_Spex, Maria Teresa Ruiz

Publications and Research

No abstract provided.

Hubble Space Telescope Images Of The Ultraluminous Supernova Remnant Complex In Ngc 6946, William P. Blair, Robert A. Fesen, Eric M. Schlegel

Dartmouth Scholarship

We present Hubble Space Telescope (HST) narrow-passband Hα and [S II] images and broadband continuum images of the region around an extremely luminous optical and X-ray supernova remnant complex in the spiral galaxy NGC 6946. These images, obtained with the PC1 CCD of the Wide Field Planetary Camera 2, show a circular, limb-brightened shell of diameter 035 [9 d/(5.1 Mpc) pc] superposed on the edge of a larger, lower surface brightness elliptical shell (14 × 08, or 34 pc × 20 pc). The HST images allow us to see that the [S II] : Hα ratio remains …

A Determination Of The Local Density Of White Dwarf Stars, J. B. Holberg, Terry D. Oswalt, E. M. Sion

Publications

The most recent version of the Catalog of Spectroscopically Identified White Dwarfs lists 2249 white dwarf stars. Among these stars are 109 white dwarfs that have either reliable trigonometric parallaxes or color-based distance moduli that place them at a distance within 20 pc of the Sun. Most of these nearby white dwarfs are isolated stars, but 28 (25% of the sample) are in binary systems, including such well-known systems as Sirius A/B and Procyon A/B. There are also three double degenerate systems in this sample of the local white dwarf population. The sample of local white dwarfs is largely complete …

Starbursts Versus Truncated Star Formation In Nearby Clusters Of Galaxies, James A. Rose, Alejandro E. E. Gaba, Nelson Caldwell, Brian Chaboyer

Dartmouth Scholarship

We present long-slit spectroscopy, B - and R -bandpass imaging, and 21 cm observations of a sample of early-type galaxies in nearby clusters, which are known to be either in a star-forming phase or to have had star formation that recently terminated. From the long-slit spectra, obtained with the Blanco 4 m telescope, we ‹nd that emission lines in the star-forming cluster galaxies are signi‹cantly more centrally concentrated than in a sample of ‹eld galaxies. The broadband imaging reveals that two currently starforming early-type galaxies in the Pegasus I cluster have blue nuclei, again indicating that recent star formation has …

10 New Γ Doradus And Δ Scuti Stars, Gregory W. Henry, Francis C. Fekel, Anthony B. Kaye, Ann Kaul

Information Systems and Engineering Management Research Publications

We present high-resolution spectroscopy and precision photometry of five new γ Doradus and five new δ Scuti variables. The five new γ Doradus variables substantially increase the number of confirmed stars of this class. All 10 stars fall in the spectral class range F0–F2, but they are cleanly separated into two groups by their luminosity and photometric periods. However, the period gap between the γ Doradus and δ Scuti stars is becoming very narrow since we confirm that HD 155154 is a γ Doradus star with the shortest periods reported to date (the shortest of its four periods is ∼0.312 …

The Long-Period Orbit Of The Dwarf Nova V630 Cassiopeiae, J. A. Orosz, J. R. Thorstensen, R. K. Honeycutt

Dartmouth Scholarship

We present extensive spectroscopy and photometry of the dwarf nova V630 Cassiopeiae. A late-type (K4-5) absorption spectrum is easily detectable, from which we derive the orbital parameters. We find a spectroscopic period of P=2.56387 +/- (4 times 10^{-5}) days and a semiamplitude of K_2=132.9 +/- 4.0 km/s. The resulting mass function, which is a firm lower limit on the mass of the white dwarf, is then f(M)=0.624 +/- 0.056 solar masses. The secondary star is a ``stripped giant'', and using relations between the core mass and the luminosity and the core mass and the radius we derive a lower limit …

Break Out Session: The Future Of White Dwarf Observing, Ted Von Hippel

Publications

On Thursday, June 15, 2000 the conference participants joined on of four afternoon break out sessions. Our break out session was charged with addressing the the following questions: Astronomy is changing. Eight to ten meter telescopes looking towards the edge of the Universe will dominate the astronomical landscape. Queue scheduling, large surveys, and the current emphasis towards the red end of the spectrum will also affect us. What consequences do these changes imply for our field? How can we convince telescope assignment committees to grand observing time to proposers from our community?

White Dwarfs In Open Clusters: New Tests Of Stellar Evolution And The Age Of The Galaxy, Ted Von Hippel

Publications

White dwarf cooling theory and very deep observations in star clusters provide a new tool to test stellar evolution theory and time scales. In particular, white dwarf cooling theory is now testing the degree of enhanced core mixing in stars with turnoff ages of 1 to 2 Gyr. More generally, I show the good overall agreement between white dwarf and modern isochrone ages over the range 0.1 to 4 Gyr.

White Dwarfs In Common Proper Motion Binary Systems: Mass Distribution And Kinematics, Nicole M. Silvestri, Terry D. Oswalt, Matt A. Wood, J. Allyn Smith, I. Neill Reid, Edward M. Sion

Publications

We present the mass distribution, gravitational redshifts, radial velocities, and space motions of white dwarf stars in common proper motion binary systems. The mass distribution we derive for the 41 DA white dwarfs in this study has a mean of 0.68 ± 0.04 M_Ꙩ. This distribution has a slightly higher mean and larger dispersion than most previous white dwarf studies. We hypothesize that this is due to a higher fraction of cool (average T_eff ̴ 10,000 K), hence old, white dwarfs in our sample. Our results indicate that samples made up of predominantly cool, old white dwarf stars …

Infrared Spectroscopy Of Symbiotic Stars. Ii. Orbits For Five S-Type Systems With Two-Year Periods, Francis C. Fekel, Kenneth H. Hinkle, Richard Joyce, Michael F. Skrutskie

Information Systems and Engineering Management Research Publications

Infrared radial velocities have been used to determine orbital elements for the cool giants of five well-known symbiotic systems, Z And, AG Dra, V443 Her, AX Per, and FG Ser, all of which have orbital periods near the two-year mean period for S-type symbiotics. The new orbits are in general agreement with previous orbits derived from optical velocities. From the combined optical and infrared velocities, improved orbital elements for the five systems have been determined. Each of the orbital periods has been determined solely from the radial-velocity data. The orbits are circular and have quite small mass functions of 0.001–0.03 …

Chromospherically Active Stars. Xviii. Sorting Out The Variability Of Hd 95559 And Gliese 410=Ds Leonis, Francis C. Fekel, Gregory W. Henry

Information Systems and Engineering Management Research Publications

We have obtained spectroscopy and photometry of HD 95559 and photometry of Gliese 410=DS Leonis. HD 95559 consists of a pair of essentially identical K1 V stars, whose orbital period we refine to 1.52599775+/-0.00000104 days. The system is photometrically variable with a mean period of 1.5264+/-0.0003 days. Despite minimum masses greater than 0.8 Msolar for each component, a search for eclipses proved negative. The lithium abundances of the components of HD 95559 indicate that the system is younger than the Hyades cluster, and its components may even have just arrived on the zero-age main sequence. Gl 410=DS Leo is also …

The Relative Age Of The Thin And Thick Galactic Disks, Wilson M. Liu, Brian Chaboyer

Dartmouth Scholarship

We determine the relative ages of the open cluster NGC 188 and selected Hipparcos field stars by isochrone fitting and compare them to the age of the thick-disk globular cluster 47 Tuc. The best-fit age for NGC 188 was determined to be 6.5 ± 1.0 Gyr. The solar-metallicity Hipparcos field stars yielded a slightly older thin-disk age, 7.5 ± 0.7 Gyr. Two slightly metal-poor ([Fe/H] = -0.22) field stars whose kinematic and orbital parameters indicate that they are members of the thin disk were found to have an age of 9.7 ± 0.6 Gyr. The age for 47 Tuc was …

Hubble Space Telescope Imaging Spectrograph Observations Of The Hot White Dwarf In The Close Binary Feige 24, Stephane Vennes, Elisha F. Polomski, Thierry Lanz, John R. Thorstensen

Dartmouth Scholarship

We obtained and analyzed two Hubble Space Telescope Imaging Spectrograph spectra of the white dwarf in the DA plus dMe binary Feige 24. The spectra, obtained at orbital quadratures, provide new estimates of the white dwarf motion and gravitational redshift resulting in revised white dwarf parameters. An analysis of interstellar absorption lines reveals the presence of two clouds (+3.1 km s-1, +17.6 km s-1) in the line of sight toward Feige 24; one of these clouds (+17.6 km s-1) is identified with the "local cloud." A study of the Lyα H I and D I interstellar medium lines shows that …

Astrophysical Quantities Of Cepheid Variables Measured With The Navy Prototype Optical Interferometer, Tyler E. Nordgren, J. T. Armstrong, M. E. Germain, R. B. Hindsley, Arsen R. Hajian, Jeffrey J. Sudol, C. A. Hummel

Physics & Engineering Faculty Publications

No abstract provided.

Time Series Analysis Of V815 Herculis Photometry Between 1984 And 1998, Lauri Jetsu, Thomas Hackman, Douglas S. Hall, Gregory W. Henry, Mariitta Kokko, J. You

Information Systems and Engineering Management Research Publications

As a case study of the solar-stellar connection, we have analysed a prolonged time series of BV photometry of the chromospherically active binary V815 Her . The surface differential rotation in the rapidly rotating G5{v} primary caused changes of 4.6% in the seasonal photometric rotation periods. This would imply a differential rotation coefficient of k = 0.184, if the rotation of the starspots follows the solar law of differential rotation and the activity is confined within the same latitudinal range as in the Sun, having k = 0.189 and the spectral-type of G2{v}. Our analysis of the primary and secondary …

Two K Giants With Supermeteoritic Lithium Abundances: Hde 233517 And Hd 9746, Suchitra C. Balachandran, Francis C. Fekel, Gregory W. Henry, Han Uitenbroek

Information Systems and Engineering Management Research Publications

Two unusual Li-rich K giants, HDE 233517 and HD 9746, have been studied. Optical spectroscopy and photometry have been obtained to determine the fundamental parameters of HDE 233517, a single K2 III with an extremely large infrared excess. The spectra yield Teff=4475 K, logg=2.25, [Fe/H]=-0.37, vsini=17.6 km s-1, and a non-LTE logɛ(7Li)=4.22. Photometric observations reveal low-amplitude light variability with a period of 47.9 days. Combined with other parameters, this results in a minimum radius of 16.7 Rsolar and minimum distance of 617 pc. Comparison of spectra obtained in 1994 and 1996 show profile variations in Hα and the Na D …

Photometric Variability In A Sample Of 187 G And K Giants, Gregory W. Henry, Francis C. Fekel, Stephen M. Henry, Douglas S. Hall

Information Systems and Engineering Management Research Publications

We have used three automatic photoelectric telescopes to obtain photometric observations of 187 G, K, and (a few) M0 field giants. We find low-amplitude photometric variability on timescales of days to weeks on both sides of the coronal dividing line (CDL) in a total of 81 or 43% of the 187 giants. About one-third of the variables have amplitudes greater than 0.01 mag in V. In our sample the percentage of variable giants is a minimum for late-G spectral classes and increases for earlier and later classes; all K5 and M0 giants are variable. We also obtained high-resolution, red wavelength …

The White Dwarf Cooling Age Of The Open Cluster Ngc 2420, Ted Von Hippel, Gerard Gilmore

Publications

We have used deep HST WFPC2 observations of two fields in NGC 2420 to produce a cluster color-magnitude diagram down to V ≈ 27. After imposing morphological selection criteria we find eight candidate white dwarfs in NGC 2420. Our completeness estimates indicate that we have found the terminus of the WD cooling sequence. We argue that the cluster distance modulus is likely to be close to 12.10 with E(B-V) = 0.04. With these parameters we find a white dwarf cooling age for NGC 2420 of 2.0 ± 0.20 (1 σ) Gyr. The 0.20 Gyr uncertainty includes errors in the photometry, …

Low-Mass Spectroscopic Binaries In The Hyades: A Candidate Brown Dwarf Companion, I. Neill Reid, S. Mahoney

Dartmouth Scholarship

We have used the HIRES echelle spectrograph on the Keck I telescope to obtain high-resolution spectroscopy of 51 late-type M dwarfs in the Hyades cluster. Cross-correlating the calibrated data against spectra of white dwarfs allows us to determine heliocentric velocities with an accuracy of ±0.3 km s⁻¹. 27 stars were observed at two epochs in 1997; two stars, RHy 42 and RHy 403, are confirmed spectroscopic binaries. RHy 42 is a double-lined, equal-mass system; RHy 403 is a single-lined, short-period binary, P∼1.275 d. RHy 403A has an absolute magnitude of M_I=10.85, consistent with a mass …

Rosat Hri And Asca Observations Of The Spiral Galaxy Ngc 6946 And Its Northeast Complex Of Luminous Supernova Remnants, Eric M. Schlegel, William P. Blair, Robert A. Fesen

Dartmouth Scholarship

Analysis of 80 ks ASCA and 60 ks ROSAT HRI observations of the face-on spiral galaxy NGC 6946 are presented. The ASCA image is the first observation of this galaxy above ~2 keV. Diffuse emission may be present in the inner ~4' extending to energies above ~2–3 keV. In the HRI data, 14 pointlike sources are detected, the brightest two being a source very close to the nucleus and a source to the northeast that corresponds to a luminous complex of interacting supernova remnants (SNRs). We detect a point source that lies ~30'' west of the SNR complex but with …

Orbital Period Of The Low‐Inclination Sw Sextantis Star V442 Ophiuchi, D. W. Hoard, John R. Thorstensen, Paula Szkody

Dartmouth Scholarship

V442 Ophiuchi is a low-inclination (noneclipsing) nova-like cataclysmic variable. We have obtained medium resolution (1-3.5 Å), time-resolved optical spectroscopy of this interacting binary star spanning an interval of 4 yr, from 1995 August to 1999 June. Using an Hα radial velocity curve constructed from our combined spectroscopic data sets, we have determined that Porb = 0.1243 days for V442 Oph, breaking the long-standing 1 day alias ambiguity in its orbital period. V442 Oph shares many of the characteristics of the group of cataclysmic variables known as the SW Sextantis stars. Its Doppler tomograms and orbital phase-dependent emission-line behavior, including …

1237+6526_Opt_Lris, Adam J. Burgasser

Publications and Research

No abstract provided.

64 Orionis: Three-Dimensional Orbit And Physical Parameters, Colin D. Scarfe, David J. Barlow, Francis C. Fekel

Information Systems and Engineering Management Research Publications

We have obtained radial velocities of the components of the short-period subsystem of the B-type triple star 64 Orionis, covering a full cycle of the long-period orbit since the date of our earlier paper by Fekel & Scarfe. We use all of our radial velocities, together with available speckle interferometry, to derive a three-dimensional orbit for the long-period system. The system has orbital periods of 14.57213 days and 12.98 yr. We also determine spectroscopically a magnitude difference at 4500 Å of 1.0 ± 0.1 between the components of the close pair. Although radial velocities of the third component continue to …

The Warps Survey. Iii. The Discovery Of An X‐Ray Luminous Galaxy Cluster At Z = 0.833 And The Impact Of X‐Ray Substructure On Cluster Abundance Measurements, H. Ebeling, L. R. Jones, E. Perlman, C. Scharf, D. Horner, G. Wegner

Dartmouth Scholarship

The Wide Angle ROSAT Pointed Survey team reviews the properties and history of the discovery of Cl J0152.7-1357, an X-ray luminous, rich cluster of galaxies at a redshift of z = 0.833. At LX = 8 × 1044h ergs s-1 (0.5-2.0 keV) Cl J0152.7-1357 is the most X-ray luminous cluster known at redshifts z > 0.55. The high X-ray luminosity of the system suggests that massive clusters may begin to form at redshifts considerably greater than unity. This scenario is supported by the high degree of optical and X-ray substructure in Cl J0152.7-1357, which is similarly complex as that …

Infrared Spectroscopy Of Symbiotic Stars. I. Orbits For Well-Known S-Type Systems, Francis C. Fekel, Richard Joyce, Kenneth H. Hinkle, Michael F. Skrutskie

Information Systems and Engineering Management Research Publications

First results are reported for a program of monitoring symbiotic-star velocities in the 1.6 μm region with infrared-array technology. Infrared radial velocities have been used to determine single-lined spectroscopic orbits for six well-known symbiotic stars, EG And, T CrB, CI Cyg, BX Mon, RS Oph, and AG Peg. The new orbits are in general agreement with previous orbits derived from optical velocities. From the combined optical and infrared velocities improved orbital elements for the six systems have been determined. Each of the orbital periods has been determined solely from the radial-velocity data. With the addition of our new velocities, the …

Spectroscopy And Orbital Periods Of The Old Novae V533 Herculis, V446 Herculis And X Serpentis, J. R. Thorstensen, C. J. Taylor

Dartmouth Scholarship

We report spectroscopic orbital periods of 0.147 d (= 3.53 h) for V533 Her, 0.207 d (= 4.97 h) for V446 Her and 1.478 d for X Ser. V533 Her (Nova Herculis 1963) shows absorption features in its He i and Balmer lines which appear only in a limited range of orbital phase, suggesting that it is a low-inclination SW Sextantis star. V446 Her is unusual in that it has started normal dwarf nova eruptions after a nova outburst, but we find nothing else unusual about it — in particular, a distance estimate based on its dwarf nova outbursts agrees …

A Newly-Discovered Cataclysmic Binary Near The Rosat Galactic Plane Source Rx J1910.8+2856, J R. Thorstensen, F Haberl

Dartmouth Scholarship

We report the discovery of a new cataclysmic binary star from the ROSAT Galactic Plane Survey. The star has V >∼ 18.5atminimumlightandwehavemeasureditasbrightasV = 15.7. Spectroscopy shows broad hydrogen and helium emission lines; HeII λ4686 is not detected. Hα radial velocities yield an orbital period of 0.1429 ± 0.0004 d (3.430 ± 0.010 h). Time- series photometry covering one orbital cycle near maximum light shows irregular variability, but no evidence of an eclipse. ThesystemappearstobeanewdwarfnovaoftheUGemorZ Cam type, and is unlikely to be a magnetic system. Its period is unusually short for a U Gem star.

Curiously, the new cataclysmic binary is 83′′ …