Jocelyn Tomkin

The carbon-to-oxygen ratio in halo dwarfs

We have used four C I lines at 9100 A and the O I triplet at 7770 A to determine C and O abundances in a sample of 34 field halo dwarfs, which span the metallicity range −3.0 ≤ [Fe/H] ≤ −0.8. The C I line enable us to obtain, for the first time, C abundances for these metal-deficient stars that are based on atomic, rather than molecular, lines. Additional observations of Fe I and Fe II lines at 4500 and 5200 A have been used to help determine atmosphere parameters of the stars

Rubidium in Metal-deficient Disk and Halo Stars

We report the first extensive study of stellar Rb abundances. High-resolution spectra have been used to determine, or set upper limits on, the abundances of this heavy element and the associated elements Y, Zr, and Ba in 44 dwarfs and giants with metallicities spanning the range -2.0 < [Fe/H] < 0.0. In metal-deficient stars Rb is systematically overabundant relative to Fe; we find an average [Rb/Fe] of +0.21 for the 32 stars with [Fe/H] < -0.5 and measured Rb. This behavior contrasts with that of Y, Zr, and Ba, which, with the exception of three new CH stars (HD 23439A and B and BD +5°3640), are consistently slightly deficient relative to Fe in the same stars; excluding the three CH stars, we find that the stars with [Fe/H] < -0.5 have average [Y/Fe], [Zr/Fe], and [Ba/Fe] of -0.19 (24 stars), -0.12 (28 stars), and -0.06 (29 stars), respectively. The different behavior of Rb on the one hand and Y, Zr, and Ba on the other can be attributed in part to the fact that in the Sun and in these stars Rb has a large r-process component while Y, Zr, and Ba are mostly s-process elements with only small r-process components. In addition, the Rb s-process abundance is dependent on the neutron density at the s-processing site. Published observations of Rb in s-process enriched red giants indicate a higher neutron density in the metal-poor giants. These observations imply a higher s-process abundance for Rb in metal-poor stars. The calculated combination of the Rb r-process abundance, as estimated for the stellar Eu abundances, and the s-process abundance, as estimated for red giants, accounts satisfactorily for the observed run of [Rb/Fe] with [Fe/H].

Nitrogen abundances in disk and halo dwarfs

High-resolution Digicon spectra of the NH band at 3360 A have been analyzed by spectrum synthesis to determine nitrogen abundances in 14 disk and halo F and G dwarfs with metal deficiencies covering the range -2.3< or =(Fe/H)< or =-0.3. We have determined carbon abundances from parallel observations and analysis of CH. In all stars nitgrogen closely follows carbon and iron; i.e., (N/C)roughly-equal0.0. We conclude that nitrogen is a primary element.

Early observations of SN 1993J in M81 at McDonald observatory

The visual light and color curves of SN 1993J show behavior unlike that of other Type II supernovae. The initial flash peaked at V=10.7 on JD=2,449,076.8, 3 days following the shock outbreak which is estimated to have occurred at JD 2,449,074.5=March 28.0 UT. High-dispersion spectra show 10 velocity components in each of the Na D lines. Early optical and IR spectra show a nearly blackbody continuum cooling from 14,900±1000 K to 11,800±700 K from March 31.2 to April 1.2 UT. Superposed on this continuum are broad, weak Balmer, Paschen, and He I lines. From blackbody fits to early spectra the color excess is estimated to be about E(B−V)=0.15±0.02

NEW PRECISION ORBITS OF BRIGHT DOUBLE-LINED SPECTROSCOPIC BINARIES. III. HD 82191, ω DRACONIS, AND 108 HERCULIS

We have determined improved spectroscopic orbits for three double-lined binaries, HD 82191 (Am), ω Dra (F5 V), and 108 Her (Am), using radial velocities from the 2.1 m telescope at McDonald Observatory, the coude feed telescope at Kitt Peak National Observatory, and 2 m telescope at Fairborn Observatory. The orbital periods range from 5.28 to 9.01 days, and all three systems have circular orbits. The new orbital dimensions (a 1 sin i and a 2 sin i) and minimum masses (m 1 sin3 i and m 2 sin3 i) have accuracies of 0.2% or better. Our improved results confirm the large minimum masses of HD 82191 and also agree with the values previously found for ω Dra. However, for the components of 108 Her our minimum masses are about 20% larger than the previous best values. We conclude that both components of HD 82191 as well as the primary of 108 Her are Am stars. However, the A9 secondary of 108 Her has normal abundances. We estimate spectral types of F4 dwarf and G0 dwarf for the components of ω Dra. The primaries of the three binaries are synchronously rotating as is the secondary of 108 Her. The secondaries of HD 82191 and ω Dra are possibly synchronously rotating.

Secondaries of eclipsing binaries. IV - The triple system Lambda Tauri

High signal-to-noise ratio Reticon observations of Lambda Tauri have been obtained along with high-quality orbital elements for both the primary and secondary of the eclipsing system. The velocity curve of the secondary is determined for the first time. The findings include: K(1) = 56.9 + or - 0.6 km/s, K(2 = 215.6 + or - 0.7 km/s, m(1) = 7.18 + or - 0.09 solar masses, and m(2) = 1.89 + or - 0.04 solar masses. The 33-day periodicity in the residuals is confirmed and is present in the secondary velocities as well as those of the primary, and can unambiguously be ascribed to orbital motion about a third body. The K and f(m) for the 33-day orbit are 10.1 + or - 0.7 km/s and 0.0034 + or - 0.0008 solar masses. The photometry shows that the orbits are coplanar to within seven degrees. The mass of the third body is 0.7 + or - 0.2 solar masses; it is most probably a K dwarf.

New Precision Orbits of Bright Double-Lined Spectroscopic Binaries. I. RR Lyncis, 12 Bootis, and HR 6169

Radial velocities from the 2.1 m telescope at McDonald Observatory supplemented with radial velocities from the coude feed telescope at Kitt Peak National Observatory provide new precise orbits for the double-lined spectroscopic binaries RR Lyn (A3/A8/A6), 12 Boo (F8 IV), and HR 6169 (A2 V). We derive orbital dimensions (a1 sin i and a2 sin i) and minimum masses (m1 i and m2 i) with accuracies of 0.06%-0.9%. The three systems, which have V magnitudes of 5.53, 4.82, and 6.42, respectively, are all sufficiently bright that they are easily within the grasp of modern optical interferometers and so afford the prospect, when our spectroscopic observations are complemented by interferometric observations, of fully determined orbits, precise masses, and distances. In the case of RR Lyn, which is also a detached eclipsing binary with a well-determined orbital inclination (i = 8745 ± 011), we are able to determine the semimajor axis of the relative orbit, a = 29.32 ± 0.04 R⊙; primary and secondary radii of 2.57 ± 0.02 and 1.59 ± 0.03 R⊙, respectively; and primary and secondary masses of 1.927 ± 0.008 and 1.507 ± 0.004 M⊙, respectively. Comparison of our new systemic velocity determination, γ = -12.03 ± 0.04 km s-1, with the earlier one of Kondo, γ = -11.61 ± 0.30 km s-1, shows no evidence of any change in the systemic velocity in the 40 yr separating the two measurements, a null result that neither confirms nor contradicts the presence of the low-mass third component proposed by Khaliullin & Khaliullina. Our spectroscopic orbit of 12 Boo is more precise than that of Boden et al. but confirms their results about this system. Our analysis of HR 6169 has produced a major improvement in its orbital elements. The minimum masses of the primary and secondary are 2.20 ± 0.01 and 1.64 ± 0.02 M⊙, respectively. Although all three systems have eccentric orbits, the six components of the systems are either pseudosynchronously rotating or very nearly so.

Spectroscopic detection of the secondaries of the Hyades interferometric spectroscopic binary theta(sup 2) Tauri and of the interferometric spectroscopic binary alpha Andromedae

We report new high-resolution, wide-wavelength-coverage CCD observations of the visual and near-infrared spectra of the interferometric spectroscopic binaries theta(sup 2) Tau (primary spectral type A 7 III) and alpha And (primary spectral type B8 IVpMnHg), which allow the first direct spectroscopic detection of their secondaries. We have measured primary and secondary radial velocities and used them to redetermine the spectroscopic orbits of the primaries, make an improved determination of K(sub 2) for theta(sup 2) Tau, and measure K(sub 2) for alpha And for the first time. The spectroscopic orbits combined with the interferometrically measured visual orbits of theta(sup 2) Tau and alpha And provide masses and distances, M(sub 1) = 2.1 +/- 0.3 solar mass, M(sub 2) = 1.6 +/- 0.2 solar mass, and d = 44.1 +/- 2.2 pc for theta(sup 2) Tau and M(sub 1) = 5.5 +/- 0.5 solar mass, M(sub 2) = 2.3 +/- 0.2 solar mass, and d = 34.0 +/- 1.3 pc for alpha And. The distance to theta(sup 2) Tau and a foreground correction of 0.07 +/- 0.05 mag set the distance to the center of the Hyades cluster at 45.5 +/- 2.5 pc, or m - M = 3.29 +/- 0.12. Indirect estimates of the mass of theta(sup 2) Taus primary, made via the mass-luminosity relation and via the Hyades cluster turnoff mass, are consistent with these dynamical masses for its primary and secondary. But in the case of alpha And, the mass-luminosity relation suggests that our dynamical masses for its primary and secondary may be too large. For alpha And somewhat smaller dynamical masses (4.0 and 1.9 solar mass) and the correspondingly smaller distance (31 pc), required by the corresponding larger orbital parallax, provide results consistent with the mass-luminosity relation for normal stars.

HR 266=ADS 784 : an early type spectroscopic, speckle astrometric multiple system

The star HR 266 is thought to be a quadruple system of « Hierarchy 3 ». The short-period binary, with components Ba and Bb, has a period of 4.241 148±0.000 008 d. The close pair orbits an unseen companion, Bc, with a period of 1769±10 d. This companion has been detected independently by spectroscopic and speckle observations. The long-period or visual orbit of this triple and component A has a period of 83.10±0.20 yr. The speckle detection of Bc as a submotion in the long-period orbit represents the first detection of a « speckle astrometric » system. Two possible models of the systems components are considered

HR 8257: A Three-Dimensional Orbit And Basic Properties

We have used interferometric and spectroscopic observations of HR 8257 to determine a three-dimensional orbit of the system. The orbit has a period of 12.21345 days and an eccentricity of 0.2895. The masses of the F0 and F2 dwarf components are 1.56 and 1.38 M☉ , respectively, with fractional errors of 1.4%. Our orbital parallax of 13.632 ± 0.095 mas, corresponding to a distance of 73.4 ± 0.6 pc, differs from the Hipparcos result by just 2% and has a significantly smaller uncertainty. From our spectroscopic observations and spectral energy distribution modeling we determine the component effective temperatures and luminosities to be T_eff(A) = 7030 ± 200 K and T_(eff)(B) = 6560 ± 200 K and L_A = 9.4 ± 0.3 L☉ and L_B = 4.7 ± 0.2 L☉ . The primary rotates pseudosynchronously, while the secondary is not far from its pseudosynchronous rotational velocity. Although both early-F stars are slowly rotating, neither component of this close binary is an Am star. A comparison with evolutionary tracks indicates that the stars are slightly metal poor, and although the components have evolved away from the zero-age main sequence, they are both still dwarfs.