arXiv subjects

G. Fritz Benedict

Publications and source records attributed to G. Fritz Benedict.

At least 19 recordsLinked to original sources

arXiv2022

The eta Aquilae System: Radial Velocities and Astrometry in Search of eta Aql B

The classical Cepheid eta Aql was not included in past Leavitt Law work (Benedict et al. 2007) because of a presumed complicating orbit due to a known B9.8V companion. To determine the orbit of eta Aql B, we analyze a significant number of radial velocity measures (RV) from eight sources. With these we establish the RV variation due to Cepheid pulsation, using a twelve Fourier coefficient model, while solving for velocity offsets required to bring the RV data sets into coincidence. RV residuals provide no evidence of orbital motion, suggesting either nearly face-on orientation or very long period. Reanalysis of Hubble Space Telescope Fine Guidance Sensor astrometry now includes reference star parallax and proper motion priors from Gaia EDR3. As modeling confirmation, we reanalyze zeta Gem in parallel, deriving zeta Gem parallax and proper motion values consistent with Gaia EDR3, and consistent with the Benedict 2007 Leavitt Law. In an effort to further characterize eta Aql B, we hypothesize that eta Aql residuals larger than those of the associated reference stars or a parallax inconsistent with EDR3 and the Benedict 2007 Leavitt Law indicate unmodeled orbital motion. Using the astrometric noise or parallax mismatch with EDR3 we estimate possible periods and mass for eta Aql B. Ascribing photocenter motion to the photometric variation of the Cepheid, eta Aql A, yields a plausible separation, consistent with a long period, explaining the lack of RV variation. None of these approaches yields an unassailable characterization of the eta Aql A-B system

astro-ph.SR↗

arXiv2021

Precision Millimeter Astrometry of the $α$ Centauri AB System

$α$ Centauri A is the closest solar-type star to the Sun and offers the best opportunity to find and ultimately to characterize an Earth-sized planet located in its Habitable Zone (HZ). Here we describe initial results from an ALMA program to search for planets in the $α$ Cen AB system using differential astrometry at millimeter wavelengths. Our initial results include new absolute astrometric measurements of the proper motion, orbital motion, and parallax of the $α$ Cen system. These lead to an improved knowledge of the physical properties of both $α$ Cen A and B. Our estimates of ALMA's relative astrometric precision suggest that we will ultimately be sensitive to planets of a few 10s of Earth mass in orbits from 1-3 AU, where stable orbits are thought to exist.

astro-ph.SR↗

arXiv2021

Dissecting the Quadruple Binary Hyad vA 351 -- Masses for three M Dwarfs and a White Dwarf

We extend results first announced by Franz et al. (1998), that identified vA 351 = H346 in the Hyades as a multiple star system containing a white dwarf. With Hubble Space Telescope Fine Guidance Sensor fringe tracking and scanning, and more recent speckle observations, all spanning 20.7 years, we establish a parallax, relative orbit, and mass fraction for two components, with a period, $P=2.70$y and total mass 2.1 Msun. With ground-based radial velocities from the McDonald Observatory Otto Struve 2.1m telescope Sandiford Spectrograph, and Center for Astrophysics Digital Speedometers, spanning 37 years, we find that component B consists of BC, two M dwarf stars orbiting with a very short period (P_ BC=0.749 days), having a mass ratio M_C/M_B=0.95. We confirm that the total mass of the system can only be reconciled with the distance and component photometry by including a fainter, higher mass component. The quadruple system consists of three M dwarfs (A,B,C) and one white dwarf (D). We determine individual M dwarf masses M_A=0.53+/-0.10 Msun, M_B=0.43+/-0.04Msun, and M_C=0.41+/-0.04Msun. The WD mass, 0.54+/-0.04Msun, comes from cooling models, an assumed Hyades age of 670My, and consistency with all previous and derived astrometric, photometric, and RV results. Velocities from H-alpha and He I emission lines confirm the BC period derived from absorption lines, with similar (He I) and higher (H-alpha) velocity amplitudes. We ascribe the larger H-alpha amplitude to emission from a region each component shadows from the other, depending on the line of sight.

astro-ph.SR↗

arXiv2017

HD 202206 : A Circumbinary Brown Dwarf System

With Hubble Space Telescope Fine Guidance Sensor astrometry and previously published radial velocity measures we explore the exoplanetary system HD 202206. Our modeling results in a parallax, $π_{abs} = 21.96\pm0.12$ milliseconds of arc, a mass for HD 202206 B of M$_B = 0.089^{ +0.007}_{-0.006}$ Msun, and a mass for HD 202206 c of M$_c = 17.9 ^{ +2.9}_{-1.8}$ MJup. HD 202206 is a nearly face-on G+M binary orbited by a brown dwarf. The system architecture we determine supports past assertions that stability requires a 5:1 mean motion resonance (we find a period ratio, $P_c/P_B = 4.92\pm0.04$) and coplanarity (we find a mutual inclination, Phi = 6 \arcdeg \pm 2 \arcdeg).

astro-ph.SR↗

arXiv2016

Astrometry with Hubble Space Telescope Fine Guidance Sensors - A Review

Over the last 20 years Hubble Space Telescope Fine Guidance Sensor interferometric astrometry has produced precise and accurate parallaxes of astrophysical interesting stars and mass estimates for stellar companions. We review parallax results, and binary star and exoplanet mass determinations, and compare a subset of these parallaxes with preliminary Gaia results. The approach to single-field relative astrometry described herein may continue to have value for targets fainter than the Gaia limit in the coming era of 20-30m telescopes.

astro-ph.SR↗

arXiv2014

The 3-dimensional architecture of the Upsilon Andromedae planetary system

The Upsilon Andromedae system is the first exoplanetary system to have the relative inclination of two planets' orbital planes directly measured, and therefore offers our first window into the 3-dimensional configurations of planetary systems. We present, for the first time, full 3-dimensional, dynamically stable configurations for the 3 planets of the system consistent with all observational constraints. While the outer 2 planets, c and d, are inclined by about 30 degrees, the inner planet's orbital plane has not been detected. We use N-body simulations to search for stable 3-planet configurations that are consistent with the combined radial velocity and astrometric solution. We find that only 10 trials out of 1000 are robustly stable on 100 Myr timescales, or about 8 billion orbits of planet b. Planet b's orbit must lie near the invariable plane of planets c and d, but can be either prograde or retrograde. These solutions predict b's mass is in the range 2 - 9 $M_{Jup}$ and has an inclination angle from the sky plane of less than 25 degrees. Combined with brightness variations in the combined star/planet light curve ("phase curve"), our results imply that planet b's radius is about 1.8 $R_{Jup}$, relatively large for a planet of its age. However, the eccentricity of b in several of our stable solutions reaches values greater than 0.1, generating upwards of $10^{19}$ watts in the interior of the planet via tidal dissipation, possibly inflating the radius to an amount consistent with phase curve observations.

astro-ph.EP↗

arXiv2014

A Technique to Derive Improved Proper Motions for Kepler Objects of Interest

We outline an approach yielding proper motions with higher precision than exists in present catalogs for a sample of stars in the Kepler field. To increase proper motion precision we combine first moment centroids of Kepler pixel data from a single Season with existing catalog positions and proper motions. We use this astrometry to produce improved reduced proper motion diagrams, analogous to a Hertzsprung-Russell diagram, for stars identified as Kepler Objects of Interest. The more precise the relative proper motions, the better the discrimination between stellar luminosity classes. With UCAC4 and PPMXL epoch 2000 positions (and proper motions from those catalogs as quasi-bayesian priors) astrometry for a single test Channel (21) and Season (0) spanning two years yields proper motions with an average per-coordinate proper motion error of 1.0 millisecond of arc per year, over a factor of three better than existing catalogs. We apply a mapping between a reduced proper motion diagram and an HR diagram, both constructed using HST parallaxes and proper motions, to estimate Kepler Object of Interest K-band absolute magnitudes. The techniques discussed apply to any future small-field astrometry as well as the rest of the Kepler field.

astro-ph.IM↗

arXiv2013

HST Fine Guidance Sensor Parallaxes for Four Classical Novae

We have used data obtained with the Fine Guidance Sensors on the Hubble Space Telescope to derive precise astrometric parallaxes for four classical novae: V603 Aql, DQ Her, GK Per, and RR Pic. All four objects exceeded the Eddington limit at visual maximum. Re-examination of the original light curve data for V603 Aql and GK Per has led us to conclude that their visual maxima were slightly brighter than commonly assumed. With known distances, we examine the various maximum magnitude--rate of decline (MMRD) relationships that have been established for classical novae. We find that these four objects show a similar level of scatter about these relationships as seen in larger samples of novae whose distances were determined using indirect techniques. We also examine the nebular expansion parallax method, and find that it fails for three of the four objects. In each case it was possible to find an explanation for the failure of that technique to give precise distance estimates. DQ Her appears to suffer from an anomalously high extinction when compared to field stars on its sight line. We suggest that this is likely due to local material, which may also be the source of the IRAS detections of this object.

astro-ph.SR↗

arXiv2011

Distance Scale Zero-Points from Galactic RR Lyrae Star Parallaxes

We present new absolute trigonometric parallaxes and proper motions for seven Pop II variable stars: five RR Lyr variables; RZ Cep, XZ Cyg, SU Dra, RR Lyr, UV Oct; and two type 2 Cepheids; VY Pyx and κ Pav. We obtained these results with astrometric data from Fine Guidance Sensors, white-light interfer- ometers on Hubble Space Telescope. We find absolute parallaxes in milliseconds of arc: RZ Cep, 2.12\pm0.16 mas; XZ Cyg, 1.67\pm0.17 mas; SU Dra, 1.42\pm0.16 mas; RR Lyr, 3.77\pm0.13 mas; UV Oct, 1.71\pm0.10 mas; VY Pyx, 6.44\pm0.23 mas; and κ Pav, 5.57\pm0.28 mas; an average σπ/π = 5.4%. With these parallaxes we compute absolute magnitudes in V and K bandpasses corrected for interstellar extinction and Lutz-Kelker-Hanson bias. Using these RRL absolute magnitudes, we then derive zero-points for MV -[Fe/H] and MK -[Fe/H]-Log P relations. The technique of reduced parallaxes corroborates these results. We employ our new results to determine distances and ages of several Galactic globular clusters and the dis- tance of the LMC. The latter is close to that previously derived from Classical Cepheids uncorrected for any metallicity effect, indicating that any such effect is small. We also discuss the somewhat puzzling results obtained for our two type 2 Cepheids.

astro-ph.SR↗

arXiv2011

Astrometry with the Hubble Space Telescope: Trigonometric Parallaxes of Selected Hyads

We present absolute parallaxes and proper motions for seven members of the Hyades open cluster, pre-selected to lie in the core of the cluster. Our data come from archival astrometric data from FGS 3, and newer data for 3 Hyads from FGS 1R, both white-light interferometers on the Hubble Space Telescope (HST). We obtain member parallaxes from six individual Fine Guidance Sensor (FGS) fields and use the field containing van Altena 622 and van Altena 627 (= HIP 21138) as an example. Proper motions, spectral classifications and VJHK photometry of the stars comprising the astrometric refer- ence frames provide spectrophotometric estimates of reference star absolute parallaxes. Introducing these into our model as observations with error, we determine absolute parallaxes for each Hyad. The parallax of vA 627 is significantly improved by including a perturbation orbit for this previously known spectroscopic binary, now an astrometric binary. Compared to our original (1997) determina- tions, a combination of new data, updated calibration, and improved analysis lowered the individual parallax errors by an average factor of 4.5. Comparing parallaxes of the four stars contained in the Hipparcos catalog, we obtain an average factor of 11 times improvement with the HST . With these new results, we also have better agreement with Hipparcos for the four stars in common. These new parallaxes provide an average distance for these seven members, < D > = 47.5 pc, for the core a \pm 1 - σ dispersion depth of 3.6 pc, and a minimum depth from individual components of 16.0 \pm 0.9 pc. Absolute magnitudes for each member are compared to established main sequences, with excellent agreement. We obtain a weighted average distance modulus for the core of the Hyades of m-M=3.376 \pm 0.01, a value close to the previous Hipparcos values, m-M=3.33\pm 0.02.

astro-ph.SR↗

arXiv2010

Origin and Dynamics of the Mutually Inclined Orbits of Upsilon Andromedae c and d

We evaluate the orbital evolution and several plausible origins scenarios for the mutually inclined orbits of Upsilon Andromedae c and d. These two planets have orbital elements that oscillate with large amplitudes and lie close to the stability boundary. This configuration, and in particular the observed mutual inclination, demands an explanation. The planetary system may be influenced by a nearby low-mass star, Upsilon And B, which could perturb the planetary orbits, but we find it cannot modify two coplanar orbits into the observed mutual inclination of ~30 deg. However, it could incite ejections or collisions between planetary companions that subsequently raise the mutual inclination to >30 deg. Our simulated systems with large mutual inclinations tend to be further from the stability boundary than Upsilon And, but we are able to produce similar systems. We conclude that scattering is a plausible mechanism to explain the observed orbits of Upsilon And c and d, but we cannot determine whether the scattering was caused by instabilities among the planets themselves or by perturbations from Upsilon And B. We also develop a procedure to quantitatively compare numerous properties of the observed system to our numerical models. Although we only implement this procedure to Upsilon And, it may be applied to any exoplanetary system.

astro-ph.EP↗

arXiv2010

Modeling Multi-Wavelength Stellar Astrometry. I. SIM Lite Observations of Interacting Binaries

Interacting binaries consist of a secondary star which fills or is very close to filling its Roche lobe, resulting in accretion onto the primary star, which is often, but not always, a compact object. In many cases, the primary star, secondary star, and the accretion disk can all be significant sources of luminosity. SIM Lite will only measure the photocenter of an astrometric target, and thus determining the true astrometric orbits of such systems will be difficult. We have modified the Eclipsing Light Curve code (Orosz & Hauschildt 2000) to allow us to model the flux-weighted reflex motions of interacting binaries, in a code we call REFLUX. This code gives us sufficient flexibility to investigate nearly every configuration of interacting binary. We find that SIM Lite will be able to determine astrometric orbits for all sufficiently bright interacting binaries where the primary or secondary star dominates the luminosity. For systems where there are multiple components that comprise the spectrum in the optical bandpass accessible to SIM Lite, we find it is possible to obtain absolute masses for both components, although multi-wavelength photometry will be required to disentangle the multiple components. In all cases, SIM Lite will at least yield accurate inclinations, and provide valuable information that will allow us to begin to understand the complex evolution of mass-transferring binaries. It is critical that SIM Lite maintains a multi-wavelength capability to allow for the proper deconvolution of the astrometric orbits in multi-component systems.

astro-ph.SR↗

arXiv2010

The Mass of HD 38529 c from Hubble Space Telescope Astrometry and High-Precision Radial Velocities

(Abridged) Hubble Space Telescope (HST) Fine Guidance Sensor astrometric observations of the G4 IV star HD 38529 are combined with the results of the analysis of extensive ground-based radial velocity data to determine the mass of the outermost of two previously known companions. Our new radial velocities obtained with the Hobby-Eberly Telescope and velocities from the Carnegie-California group now span over eleven years. With these data we obtain improved RV orbital elements for both the inner companion, HD 38529 b and the outer companion, HD 38529 c. We identify a rotational period of HD 38529 (P_{rot}=31.65 +/- 0.17 d) with FGS photometry. We model the combined astrometric and RV measurements to obtain the parallax, proper motion, perturbation period, perturbation inclination, and perturbation size due to HD 38529 c. For HD 38529 c we find P = 2136.1 +/- 0.3 d, perturbation semi-major axis α=1.05 +/-0.06$ mas, and inclination $i$ = 48.3 deg +/- 4 deg. Assuming a primary mass M_* = 1.48 M_{sun}, we obtain a companion mass M_c = 17.6 ^{+1.5}_{-1.2} M_{Jup}, 3-sigma above a 13 M_{Jup} deuterium burning, brown dwarf lower limit. Dynamical simulations incorporating this accurate mass for HD 38529 c indicate that a near-Saturn mass planet could exist between the two known companions. We find weak evidence of an additional low amplitude signal that can be modeled as a planetary-mass (~0.17 M$_{Jup}) companion at P~194 days. Additional observations (radial velocities and/or Gaia astrometry) are required to validate an interpretation of HD 38529 d as a planetary-mass companion. If confirmed, the resulting HD 38529 planetary system may be an example of a "Packed Planetary System".

astro-ph.SR↗

arXiv2009

The Mass of the Candidate Exoplanet Companion to HD136118 from Hubble Space Telescope Astrometry and High-Precision Radial Velocities

We use Hubble Space Telescope Fine Guidance Sensor astrometry and high-cadence radial velocities for HD136118 from the HET with archival data from Lick to determine the complete set of orbital parameters for HD136118b. We find an orbital inclination for the candidate exoplanet of i_{b} = 163.1 +- 3.0 deg. This establishes the actual mass of the object, M_{b} = 42^{+11}_{-18} MJup, in contrast to the minimum mass determined from the radial velocity data only, M_{b}sin{i} ~ 12 MJup. Therefore, the low-mass companion to HD 136118 is now identified as a likely brown dwarf residing in the "brown dwarf desert".

astro-ph.SR↗

arXiv2009

Astrometry with the Hubble Space Telescope: Trigonometric Parallaxes of Planetary Nebula Nuclei: NGC 6853, NGC 7293, Abell 31, and DeHt 5

We present absolute parallaxes and relative proper motions for the central stars of the planetary nebulae NGC 6853 (The Dumbbell), NGC 7293 (The Helix), Abell 31, and DeHt 5. This paper details our reduction and analysis using DeHt 5 as an example. We obtain these planetary nebula nuclei (PNNi) parallaxes with astrometric data from Fine Guidance Sensors FGS 1R and FGS 3, white-light interferometers on the Hubble Space Telescope (HST). Proper motions, spectral classifications and VJHKT_2M and DDO51 photometry of the stars comprising the astrometric reference frames provide spectrophotometric estimates of reference star absolute parallaxes. Introducing these into our model as observations with error, we determine absolute parallaxes for each PNN. Weighted averaging with previous independent parallax measurements yields an average parallax precision, σ_π/π= 5 %. Derived distances are: d_{NGC 6853}=405^{+28}_{-25}pc, d_{NGC 7293}=216^{+14}_{-12} pc, d_{Abell 31} = 621^{+91}_{-70} pc, and d_{DeHt 5} = 345^{+19}_{-17} pc. These PNNi distances are all smaller than previously derived from spectroscopic analyses of the central stars. Derived absolute magnitudes and previously measured effective temperatures permit estimates of PNNi radii, through both the Stefan-Boltzmann relation and Eddington fluxes. Comparing absolute magnitudes with post-AGB models provides mass estimates. Masses cluster around 0.57 M(sun), close to the peak of the white dwarf mass distribution. Adding a few more PNNi with well-determined distances and masses, we compare all the PNNi with cooler white dwarfs of similar mass, and confirm, as expected, that PNNi have larger radii than white dwarfs that have reached their final cooling tracks. (Abridged)

astro-ph.SR↗

arXiv2009

Astrometry - Challenging our Understanding of Stellar Structure and Evolution

Stellar mass plays a central role in our understanding of star formation and aging. Stellar astronomy is largely based on two maps, both dependent on mass, either indirectly or directly: the Hertzprung-Russell Diagram (HRD) and the Mass-Luminosity Relation (MLR). The extremes of both maps, while not terra incognita, are characterized by large uncertainties. A precise HRD requires precise distance obtained by direct measurement of parallax. A precise MLR requires precise measurement of binary orbital parameters, with the ultimate goal the critical test of theoretical stellar models. Such tests require mass accuracies of ~1%. Substantial improvement in both maps requires astrometry with microsecond of arc measurement precision. Why? First, the 'tops' of both stellar maps contain relatively rare objects, for which large populations are not found until the observing horizon reaches hundreds or thousands of parsecs. Second, the 'bottoms' and 'sides' of both maps contain stars, either intrinsically faint, or whose rarity guarantees great distance, hence apparent faintness. With an extensive collection of high accuracy masses that can only be provided by astrometry with microsecond of arc measurement precision, astronomers will be able to stress test theoretical models of stars at any mass and at every stage in their aging processes.

astro-ph.SR↗

arXiv2008

HST FGS astrometry - the value of fractional millisecond of arc precision

In a few years astrometry with the venerable combination of Hubble Space Telescope and Fine Guidance Sensor will be replaced by SIM, GAIA, and long-baseline interferometry. Until then we remain a resource of choice for sub-millisecond of arc precision optical astrometry. As examples we discuss 1) the uses which can be made of our parallaxes of galactic Cepheids, and 2) the determination of perturbation orbital elements for several exoplanet host stars, yielding true companion masses.

astro-ph↗

arXiv2007

Detection of a Third Planet in the HD 74156 System Using the Hobby-Eberly Telescope

We report the discovery of a third planetary mass companion to the G0 star HD 74156. High precision radial velocity measurements made with the Hobby-Eberly Telescope aided the detection of this object. The best fit triple Keplerian model to all the available velocity data yields an orbital period of 347 days and minimum mass of 0.4 M_Jup for the new planet. We determine revised orbital periods of 51.7 and 2477 days, and minimum masses of 1.9 and 8.0 M_Jup respectively for the previously known planets. Preliminary calculations indicate that the derived orbits are stable, although all three planets have significant orbital eccentricities (e = 0.64, 0.43, and 0.25). With our detection, HD 74156 becomes the eighth normal star known to host three or more planets. Further study of this system's dynamical characteristics will likely give important insight to planet formation and evolutionary processes.

astro-ph↗