Claud H. Sandberg Lacy

The Eclipsing Binary V1061 Cygni: Confronting Stellar Evolution Models for Active and Inactive Solar-Type Stars

We present spectroscopic and photometric observations of the eclipsing system V1061 Cyg (P = 2.35 days). A third star is visible in the spectrum, and the system is a hierarchical triple. We combine the radial velocities for the three stars, times of eclipse, and intermediate astrometric data from the Hipparcos mission (abscissa residuals) to establish the elements of the outer orbit, which is eccentric and has a period of 15.8 yr. We determine accurate values for the masses, radii, and effective temperatures of the binary components: MAa = 1.282 ± 0.015 M☉, RAa = 1.615 ± 0.017 R☉, and T = 6180 ± 100 K for the primary (star Aa), and MAb = 0.9315 ± 0.0068 M☉, RAb = 0.974 ± 0.020 R☉, and T = 5300 ± 150 K for the secondary (Ab). The mass of the tertiary is determined to be MB = 0.925 ± 0.036 M☉ and its effective temperature is T = 5670 ± 150 K. Current stellar evolution models agree well with the properties of the primary but show a very large discrepancy in the radius of the secondary, in the sense that the predicted values are ~10% smaller than observed (a ~5 σ effect). In addition, the temperature is cooler than predicted, by some 200 K. These discrepancies are quite remarkable given that the star is only 7% less massive than the Sun, the calibration point of all stellar models. We identify the chromospheric activity as the likely cause of the effect. Inactive stars agree very well with the models, while active ones such as V1061 Cyg Ab appear systematically too large and too cool.

Properties of main-sequence eclipsing binaries - Into the G stars with HS Aurigae, FL Lyrae, and EW Orionis

Spectrographic and photometric observations of three detached main sequence eclipsing binary systems with one or both components of type G, HS Aur, FL Lyr, and EW Ori, are analyzed. Ephemerides, V and R magnitudes, V-R indices, epochs, periods, e cos omega, photometric solutions, and spectrograms are presented for the systems. The radial velocities are analyzed and the orbital elements are obtained. A preliminary comparison of the systems is made with predictions from evolutionary models. HS Aur now represents a well-analyzed main sequence detached binary with both components having properties lying between those of the sun and the M1 dwarf YY Gem. In the case of FL Lyr, the two components differ significantly in their properties, making it of particular interest for its comparison with interior models and for its potential contribution to the flux and temperature scales. 37 references.

Discovery of a relationship between spiral arm morphology and supermassive black hole mass in disk galaxies

We present a relationship between spiral arm pitch angle (a measure of the tightness of spiral structure) and the mass of supermassive black holes (BHs) in the nuclei of disk galaxies. We argue that this relationship is expected through a combination of other relationships, whose existence has already been demonstrated. The recent discovery of AGN in bulgeless disk galaxies suggests that halo concentration or virial mass may be one of the determining factors in BH mass. Taken together with the result that mass concentration seems to determine spiral arm pitch angle, one would expect a relation to exist between spiral arm pitch angle and supermassive BH mass in disk galaxies, and we find that this is indeed the case. We conclude that this relationship may be important for estimating evolution in BH masses in disk galaxies out to intermediate redshifts, since regular spiral arm structure can be seen in galaxies out to z 1.

MEASUREMENT OF GALACTIC LOGARITHMIC SPIRAL ARM PITCH ANGLE USING TWO-DIMENSIONAL FAST FOURIER TRANSFORM DECOMPOSITION

A logarithmic spiral is a prominent feature appearing in a majority of observed galaxies. This feature has long been associated with the traditional Hubble classification scheme, but historical quotes of pitch angle of spiral galaxies have been almost exclusively qualitative. We have developed a methodology, utilizing two-dimensional fast Fourier transformations of images of spiral galaxies, in order to isolate and measure the pitch angles of their spiral arms. Our technique provides a quantitative way to measure this morphological feature. This will allow comparison of spiral galaxy pitch angle to other galactic parameters and test spiral arm genesis theories. In this work, we detail our image processing and analysis of spiral galaxy images and discuss the robustness of our analysis techniques.

An exact solution of the ephemeris-curve problem

We new method is presented for the determination of apsidal motion parameters from observed times of minima of eccentric eclipsing binary stars. Previous methods have relied on approximations which, in the most accurate case, include terms up to the fifth power of the eccentricity. The new method is exact − no approximations are used. Instead, iterative numerical methods are used to solve the transcendental equations to arbitrarily high precision. A Levenberg-Marquardt method is used to obtain simultaneously the optimum values of all fitting parameters and their mean errors. As an example, the method is used to analyze the apsidal motion of V523 Sgr

ABSOLUTE PROPERTIES OF THE ECLIPSING BINARY STAR RW LACERTAE

We present 3004 differential observations in the V bandpass measured by a robotic telescope, as well as 36 pairs of radial velocities from high-resolution spectroscopic observations, of the detached, eccentric, EA-type, 10.37 day period, double-lined eclipsing binary star RW Lac. Absolute dimensions of the components are determined with excellent precision (better than 0.7% in the masses and 0.5% in the radii) for the purpose of testing various aspects of theoretical modeling. We obtain 0.928 ± 0.006 M⊙ and 1.186 ± 0.004 R⊙ for the hotter, larger, more massive, and more luminous photometric primary (star A) and 0.870 ± 0.004 M⊙ and 0.964 ± 0.004 R⊙ for the cooler, smaller, less massive, and less luminous photometric secondary (star B). A faint, third component contributes 2.6% of the light in V but is not detected in our spectrograms. The effective temperatures and interstellar reddening of the stars are accurately determined from UBV and uvbyβ photometry and from analysis of the spectrograms: 5760 ± 100 K for the primary and 5560 ± 150 K for the secondary, corresponding to spectral types of G5 and G7, and 0.050 mag for interstellar reddening Eb-y. The orbits are slightly eccentric, and spectral line widths give observed rotational velocities that are not significantly different from synchronous for both components. The components of RW Lac are old, somewhat metal-deficient, low-mass, main-sequence stars with an age of about 11 Gyr, according to models.

Identification of Outflows and Candidate Dual Active Galactic Nuclei in SDSS Quasars at z = 0.8-1.6

We present a sample of 131 quasars from the Sloan Digital Sky Survey at redshifts 0.8 < z < 1.6 with double peaks in either of the high-ionization narrow emission lines [Ne V] λ3426 or [Ne III] λ3869. These sources were selected with the intention of identifying high-redshift analogs of the z < 0.8 active galactic nuclei (AGNs) with double-peaked [O III] λ5007 lines, which might represent AGN outflows or dual AGNs. Lines of high ionization potential are believed to originate in the inner, highly photoionized portion of the narrow line region, and we exploit this assumption to investigate the possible kinematic origins of the double-peaked lines. For comparison, we measure the [Ne V] λ3426 and [Ne III] λ3869 double peaks in low-redshift (z < 0.8) [O III]-selected sources. We find that [Ne V] λ3426 and [Ne III] λ3869 show a correlation between line splitting and line width similar to that of [O III] λ5007 in other studies, and the velocity splittings are correlated with the quasar Eddington ratio. These results suggest an outflow origin for at least a subset of the double peaks, allowing us to study the high-ionization gas kinematics around quasars. However, we find that a non-negligible fraction of our sample show no evidence for an ionization stratification. For these sources, the outflow scenario is less compelling, leaving the dual AGN scenario as a viable possibility. Finally, we find that our sample shows an anti-correlation between the velocity-offset ratio and luminosity ratio of the components, which is a potential dynamical argument for the presence of dual AGNs. Therefore, this study serves as a first attempt at extending the selection of candidate dual AGNs to higher redshifts.

Absolute Dimensions of the Unevolved B-Type Eclipsing Binary GG Orionis

We present photometric observations in B and V, as well as spectroscopic observations of the detached, eccentric 6.6 day double-lined eclipsing binary GG Ori, a member of the Orion OB1 association. Absolute dimensions of the components, which are virtually identical, are determined to high accuracy (better than 1% in the masses and better than 2% in the radii) for the purpose of testing various aspects of theoretical modeling. We obtain MA = 2.342 ± 0.016 M⊙ and RA = 1.852 ± 0.025 R⊙ for the primary, and MB = 2.338 ± 0.017 M⊙ and RB = 1.830 ± 0.025 R⊙ for the secondary. The effective temperature of both stars is 9950 ± 200 K, corresponding to a spectral type of B9.5. GG Ori is very close to the zero-age main sequence, and comparison with current stellar evolution models gives ages of 65–82 Myr or 7.7 Myr, depending on whether the system is considered to be burning hydrogen on the main sequence or still in the final stages of pre–main-sequence contraction. Good agreement is found in both scenarios for a composition close to solar. We have detected apsidal motion in the binary at a rate of = 000061 ± 000025 cycle-1, corresponding to an apsidal period of U = 10,700 ± 4500 yr. A substantial fraction of this (~70%) is due to the contribution from general relativity, and our measurement is entirely consistent with theory. The eccentric orbit of GG Ori is well explained by tidal evolution models, but both theory and our measurements of the rotational velocity of the components are as yet inconclusive as to whether the stars are synchronized with the orbital motion.

Absolute properties of the eclipsing binary system AQ Serpentis: A stringent test of convective core overshooting in stellar evolution models

We report differential photometric observations and radial-velocity measurements of the detached, 1.69 day period, double-lined eclipsing binary AQ Ser. Accurate masses and radii for the components are determined to better than 1.8% and 1.1%, respectively, and are M 1 = 1.417 ± 0.021 M ☉, M 2 = 1.346 ± 0.024 M ☉, R 1 = 2.451 ± 0.027 R ☉, and R 2 = 2.281 ± 0.014 R ☉. The temperatures are 6340 ± 100 K (spectral type F6) and 6430 ± 100 K (F5), respectively. Both stars are considerably evolved, such that predictions from stellar evolution theory are particularly sensitive to the degree of extra mixing above the convective core (overshoot). The component masses are different enough to exclude a location in the H-R diagram past the point of central hydrogen exhaustion, which implies the need for extra mixing. Moreover, we find that current main-sequence models are unable to match the observed properties at a single age even when allowing the unknown metallicity, mixing length parameter, and convective overshooting parameter to vary freely and independently for the two components. The age of the more massive star appears systematically younger. AQ Ser and other similarly evolved eclipsing binaries showing the same discrepancy highlight an outstanding and largely overlooked problem with the description of overshooting in current stellar theory.

FURTHER EVIDENCE FOR A SUPERMASSIVE BLACK HOLE MASS-PITCH ANGLE RELATION

We present new and stronger evidence for a previously reported relationship between galactic spiral arm pitch angle P (a measure of the tightness of spiral structure) and the mass M {sub BH} of a disk galaxys nuclear supermassive black hole (SMBH). We use an improved method to accurately measure the spiral arm pitch angle in disk galaxies to generate quantitative data on this morphological feature for 34 galaxies with directly measured black hole masses. We find a relation of log (M/M {sub ☉}) = (8.21 ± 0.16) – (0.062 ± 0.009)P. This method is compared with other means of estimating black hole mass to determine its effectiveness and usefulness relative to other existing relations. We argue that such a relationship is predicted by leading theories of spiral structure in disk galaxies, including the density wave theory. We propose this relationship as a tool for estimating SMBH masses in disk galaxies. This tool is potentially superior when compared to other methods for this class of galaxy and has the advantage of being unambiguously measurable from imaging data alone.