The Einstein Redshift in White Dwarfs

Low-dispersion radial velocities of 53 white dwarfs have been measured on Palomar spectrograms. Table 1 contains the type, velocity, space-motion components, photometrically deduced temperature and radius, for each star. Table 4 contains 39 additional radial velocities of very low weight. A few members of wide binary systems and 6 white dwarfs in the Hyades provide direct measures of the Einstein gravitational redshift, with a mean value of +51 km/sec. Omitting the very-high-velocity star LP9-231, there are 37 DA stars, with a mean K-term (expansion velocity) of +65.6 km/sec. If the Hyades stars are omitted, the mean K term is +62.5 km/sec. A number of white dwarfs are members of the high-velocity population. Systematic wavelength shifts of He i lines in DB stars make their velocities more negative than those of DA stars; similar negative shifts may exist for metallic lines. The temperature scale is obtained from colors and, combined with luminosities, gives radii. The broad distribution of radii and redshifts is shown in Figure 2, and median values are derived. The median radial velocity for 37 DA stars is +58 km/sec, and the median radius 0.0107 R_⊙; the redshift and radius give a mass of 0.98 M_⊙. However, this value is almost certainly too high, if we expect accordance with the theoretical mass-radius relation. The theoretical M-R relation of a zero-temperature degenerate star predicts a redshift, for given mass, for various compositions. Two corrections could bring the theoretically expected redshifts into agreement with the observations. Either a systematic change in luminosity, ΔM_v of +0.25 mag, or a reciprocal temperature change of Δθ = —0.03, reduces the median radius to 0.0093 R_⊙. The mass derived from the redshift is then 0.86 M_⊙. These values are in accordance with the Hamada-Salpeter mass-radius relation, if the composition in the interior is pure helium. A carbon or magnesium interior also gives a radius not too different from the colorimetric radius. An iron core gives a mass of 0.73 M_⊙, but a radius of 0.008 R_⊙, sufficiently smaller to require substantial changes in the temperature scale. The mass now derived from the radial velocities is higher than that previously found from radii only and closer to the Chandrasekhar limit

Nature of BD + 17° 4708

Oke, Greenstein, and Gunn (1966) called the GO star BD + 17° 4708 a field horizontal-branch star. They determined its effective temperature to be 6000° K, and its surface gravity as log g = 3.0. In his study of field horizontal-branch stars, Newell (1969) found + 17° 4708 to be the reddest such star, and it occupied a critical position in his plot of 0_e vs. log g, serving to separate more clearly the groups he calls disk horizontal-branch and halo horizontal-branch stars. It is the purpose ofthis note to indicate that + 17° 4708 is a G subdwarf, possibly slightly evolved, rather than a field horizontal-branch star

The Nature of Faint Blue Stars in the Halo. II

Spectra and colors of 189 hot (FB) stars selected colorimetrically and mostly within 30° of the galactic poles are analyzed quantitatively for surface gravity and effective temperatures. Palomar spectra give line intensities and Balmer line profiles, found in the Appendix tables. Using a network of model atmospheres, the g and θ so determined give directly the light-to-mass ratio, and eventually the luminosities. The high-latitude hot stars cover a range of 10^6 in luminosity, and are classifiable into various groups. Spectroscopically normal B stars make up 26 percent of the sample; they rotate and have nearly normal line spectra. Interpreted as Population I stars, on the mass-luminosity relation, they have relatively high luminosities and large z-coordinates. For some, the nuclear lifetimes at present luminosities are less than transit times from the plane. Their high velocities present a problem for galactic kinematics. A few are slightly helium rich, while others are highly evolved Population II stars, from details of the spectroscopy. Some of the Population I stars may be in not-understood, short-lived evolutionary phases of high luminosity and low mass. The (g, θ)-relation can be transformed into luminosity-temperature diagrams if masses are known. Many fall along a relation log gθ^4 = 2.35, have common properties of halo stars, and T_(eff) from 9500° to 40,000° K. The light-to-mass ratio for these is 68 (in solar units) ; most HB and sdB stars have weak metal and weak helium lines, i.e., are halo stars. We call this the extended horizontal branch (EHB). Quantitative classification gives 17 percent of the FB stars as horizontal-branch B and early A (HB) stars, and 16 percent subdwarf B (sdB) stars. There are 16 percent subdwarf O (sdO) stars, including planetary nuclei; these have strong, or very strong, helium lines. Assuming a constant mass, 0.66 m_⊙, the observed L/m gives Mb = +0.5. The EHB for field stars fits the globular cluster HB, and extends it to high T_(eff). The bolometric correction produces the change of M_v with color. The hot white dwarfs are 11 percent of the FB stars and appear as a bridge between the sdO stars and the ordinary DA white dwarfs. Composite stars are unresolved, noninteracting binaries with strange UBV colors; they require a faint Mv for the primary (e.g., sdO or sdB), and an unevolved G companion. The helium deficiency and the evolutionary problems are sharpest for the EHB stars. In a few, slightly stronger helium lines are accompanied by lines of peculiar elements (S III, P II seen at high dispersion. While the L/m ratio is closely the same for sdO as for sdB and HB, the He lines become strong. Evolutionary tracks avoid the region of the hot EHB stars; the hottest sdO stars approach the helium main sequence. The low surface helium is almost certainly not cosmological in origin. Gravitational diffusion in a nonrotating star in the absence of convection is plausible; in the sdO and the peculiar sdB stars convection and helium flashes may have occurred. Numerous radial velocities were measured. Where possible, proper motions, luminosities, and radial-velocity dispersions were used for space motions. The Population I normal stars have abnormally high space motions, not greatly different from Population II stars. The luminosities derived from spectroscopy are consistent with those from peculiar motions

Interview with Jesse L. Greenstein

Interview in three sessions in 1982 with Jesse L. Greenstein, DuBridge Professor of Astrophysics, emeritus. Greenstein discusses his early career at the Yerkes Observatory of the University of Chicago, under Otto Struve (1937-1948), and his arrival at Caltech in 1948 to build an astronomy department in the Division of Physics, Mathematics, and Astronomy. He discusses the early partnership between Caltech and the Carnegie Institution of Washington in running Mount Wilson and Palomar Observatories, the interactions between observational astronomy and theoretical astrophysics, and the rise of radio astronomy. Besides his discussion of his work on stellar composition, the interview contains his recollections of such twentieth-century pioneers of astronomy and astrophysics as Struve, Grote Reber, Gerard Kuiper, Edwin Hubble, Fritz Zwicky, Walter Baade, Rudolph Minkowski, H. P. Robertson, Richard Tolman, and Fred Hoyle--and of various Caltech principals including Lee DuBridge, Earnest Watson, Arnold Beckman, and Robert Christy. He also discusses his service in the 1960s as chairman of Caltech's Faculty Board and member of its Aims and Goals Committee. He speculates about the scarcity of women astronomers and the difficulties they face. In an addendum to his interview, he discusses in more technical detail latter-day changes in instrumentation, the impact of new and improved detectors, and their contributions to his work on white dwarfs

Optical and radio astronomy in the early years

Radio noise from space was detected by Karl Jansky in 1931, working at the Bell Telephone Laboratories (Jansky 1933). This revolutionary discovery broke the barrier confining astronomical knowledge to the information contained, and the relevant physics, within the narrow band of wavelengths accessible (an octave and a half), and to positions and motions under purely gravitational forces. Jansky's wavelength was ten million times longer than that of light. His signals were radiated from the galactic center, 10,000 parsecs distant. The long wavelengths he used resulted in low angular resolution. There was no radial velocity information, no sharp spectral features (the first line was found twenty years later). For such reasons, and perhaps because he was an electrical engineer, no astronomer beat a pathway to his door; in fact I have never met any astronomer who personally knew him. Public recognition came only as an article in the New York Times (May 5, 1933) and a radio interview. His relevant bibliography includes only seven entries over the years 1932 to 1939, and he died young (see the article by Sullivan in this volume for further information on Jansky). As a summer resident of New Jersey seashore resorts in the early 1930s, I wore golf knickers, possibly even a hip flask, and drove an open car with a rumble seat (oh nostalgia!) past the giant antennas of the transatlantic radio transmitters for which Jansky's studies of noise background were to find the best operating wavelengths. Although I felt no premonitory twinges, I met my wife there, soon became interested in Jansky's results, and my life became linked with that place and time

Nucleosynthesis during the Early History of the Solar System

Abundances in terrestrial and meteoritic matter indicate that the synthesis of D^2, Li^6, Li^7, Be^9, B^(10) and B^(11) and possibly C^(13) and N^(15) occurred during an intermediate stage in the early history of the solar system. In this intermediate stage, the planetary material had become largely separated, but not completely, from the hydrogen which was the main constituent of primitive solar material. Appropriate physical conditions were satisfied by solid planetesimals of dimensions from 1 to 50 metres consisting of silicates and oxides of the metals embedded in an icy matrix. The synthesis occurred through spallation and neutron reactions simultaneously induced in the outer layers of the planetesimals by the bombardment of high energy charged particles, mostly protons, accelerated in magnetic flares at the surface of the condensing Sun. The total particle energy was approximately 10^(45) ergs while the average energy was close to 500 MeV per nucleon. Recent studies of the abundance of lithium in young T Tauri stars serve as the primary astronomical evidence for this point of view. The observed abundances of lithium and beryllium in the surface of the Sun are discussed in terms of the astronomical and nuclear considerations brought forward. The isotope ratios D^2/H^1 = 1.5 × 10^(−4), Li^6/L^i7 = 0.08, and B^(10)/B^(11) = 0.23 are the basic data leading to the requirement that 10 per cent of terrestrial-meteoritic material was irradiated with a thermal neutron flux of 10^7 n/cm^2 s for an interval of 10^7 years. The importance of the (n, α) reactions on Li^6 and B^(10) is indicated by the relatively low abundances of these two nuclei. It is shown that the neutron flux was sufficient to produce the radioactive Pd^(107) and I^(129) necessary to account for the radiogenic Ag^(107) and Xe^(129) anomalies recently observed in meteorites. The short time interval, ∼ 6 × 10^7 years, required for the radioactive decays to be effective applies to the interval between the end of nucleosynthesis in the solar system and the termination of fractionation processes in the parent bodies of the meteorites. It is not necessary to postulate a short time interval between the last event of galactic nucleosynthesis and the formation of large, solid bodies in the solar nebula

The Faint End of the Main Sequence

New infrared observations of the two faintest known, late M dwarfs, Wolf 359 and +4°4048B (=VB 10) provide accurate luminosities and moderately well-determined temperatures (2500° and 2250° K, respectively). The photometric observations are fitted to a blackbody energy distribution on the assumption that line and band blocking affect most of the spectrum below 1 μ; the temperature structure is taken as that of a gray body. The resulting data, together with Johnson's observations for dM4 and dM5 stars, which have been reanalyzed, calibrate the faint end of the main sequence, with results given in a table and a figure. The bolometric corrections are very large and increase steeply to 6 mag, so that the faintest known stars are, in fact, not very faint; Wolf 359 has L = 13 X 10^(-4) L_☉, and VB 10 has L = 5 X 10^(-4) L_☉. A statistical discussion of Luyten's faint red stars of large proper motion gives L = 4 X 10^(-4) L_☉. With a conventional mass-luminosity relation, ℳ ≥ 0.09 ℳ_☉ , for stars of known luminosity. Stars of still lower mass, such as L726-8, are difficult to interpret

Spectrum of a^2; Canum Venaticorum, 5000-6700 Å

A complete list is given of all lines observed between 5000 and 6650 Å in the spectrum of a^2 CVn. Approximately three-quarters of the features have been identified. Lines of Pb ii and P ii are not present. Lines of Gd m and Pr m vary in equivalent width and radial velocity in a manner similar to the singly ionized rare earths. Lines of Cl ii are present and also behave like those of a rare earth

The Einstein Redshift in White Dwarfs

Low-dispersion radial velocities of 53 white dwarfs have been measured on Palomar spectrograms. Table 1 contains the type, velocity, space-motion components, photometrically deduced temperature and radius, for each star. Table 4 contains 39 additional radial velocities of very low weight. A few members of wide binary systems and 6 white dwarfs in the Hyades provide direct measures of the Einstein gravitational redshift, with a mean value of +51 km/sec. Omitting the very-high-velocity star LP9-231, there are 37 DA stars, with a mean K-term (expansion velocity) of +65.6 km/sec. If the Hyades stars are omitted, the mean K term is +62.5 km/sec. A number of white dwarfs are members of the high-velocity population. Systematic wavelength shifts of He i lines in DB stars make their velocities more negative than those of DA stars; similar negative shifts may exist for metallic lines. The temperature scale is obtained from colors and, combined with luminosities, gives radii. The broad distribution of radii and redshifts is shown in Figure 2, and median values are derived. The median radial velocity for 37 DA stars is +58 km/sec, and the median radius 0.0107 R_⊙; the redshift and radius give a mass of 0.98 M_⊙. However, this value is almost certainly too high, if we expect accordance with the theoretical mass-radius relation. The theoretical M-R relation of a zero-temperature degenerate star predicts a redshift, for given mass, for various compositions. Two corrections could bring the theoretically expected redshifts into agreement with the observations. Either a systematic change in luminosity, ΔM_v of +0.25 mag, or a reciprocal temperature change of Δθ = —0.03, reduces the median radius to 0.0093 R_⊙. The mass derived from the redshift is then 0.86 M_⊙. These values are in accordance with the Hamada-Salpeter mass-radius relation, if the composition in the interior is pure helium. A carbon or magnesium interior also gives a radius not too different from the colorimetric radius. An iron core gives a mass of 0.73 M_⊙, but a radius of 0.008 R_⊙, sufficiently smaller to require substantial changes in the temperature scale. The mass now derived from the radial velocities is higher than that previously found from radii only and closer to the Chandrasekhar limit