arXiv subjects

Francis C. Fekel

Publications and source records attributed to Francis C. Fekel.

At least 19 recordsLinked to original sources

arXiv2025

Binary Parameters for the Recurrent Nova T Coronae Borealis

T CrB is among the brightest novae. It is recurrent with outbursts happening approximately every 80 years. The next outburst is imminent, expected in 2025. The T CrB binary consists of an M4 III red giant (RG) secondary and a white dwarf (WD) primary. A time series of spectra of the RG was obtained between 2022 and 2024. Radial velocities (RVs) from these data were combined with literature RVs and an updated orbit computed. The orbit is circular to a high precision and has a period of 227.5494 +/- 0.0049 days for the circular solution. An eccentric solution yields an eccentricity of 0.0072 +/- 0.0026. Rotational line broadening of the RG was also measured. Binary parameters are derived by maximum likelihood modeling of the available observational data. The WD, in accord with other estimates for recurrent novae, is massive. Assuming the Gaia distance, the WD mass is 1.37 +/- 0.01 M sun with the M giant secondary mass 0.69 +0.02/-0.01 M sun. We discuss the evolution of this system and both paths to and limitations on further refining the values of the system parameters.

astro-ph.SR↗

arXiv2022

Visual Orbits of Spectroscopic Binaries with the CHARA Array. IV. HD 61859, HD 89822, HD 109510, and HD 191692

We present the visual orbits of four spectroscopic binary stars, HD 61859, HD 89822, HD 109510, and HD 191692, using long baseline interferometry with the CHARA Array. We also obtained new radial velocities from echelle spectra using the APO 3.5 m, CTIO 1.5 m, and Fairborn Observatory 2.0 m telescopes. By combining the astrometric and spectroscopic observations, we solve for the full, three-dimensional orbits and determine the stellar masses to 1-12% uncertainty and distances to 0.4-6% uncertainty. We then estimate the effective temperature and radius of each component star through Doppler tomography and spectral energy distribution analyses. We found masses of 1.4-3.5 Msun, radii of 1.5-4.7 Rsun, and temperatures of 6400-10300K. We then compare the observed stellar parameters to the predictions of the stellar evolution models, but found that only one of our systems fits well with the evolutionary models.

astro-ph.SR↗

arXiv2022

ARMADA II: Further Detections of Inner Companions to Intermediate Mass Binaries with Micro-Arcsecond Astrometry at CHARA and VLTI

We started a survey with CHARA/MIRC-X and VLTI/GRAVITY to search for low mass companions orbiting individual components of intermediate mass binary systems. With the incredible precision of these instruments, we can detect astrometric "wobbles" from companions down to a few tens of micro-arcseconds. This allows us to detect any previously unseen triple systems in our list of binaries. We present the orbits of 12 companions around early F to B-type binaries, 9 of which are new detections and 3 of which are first astrometric detections of known RV companions. The masses of these newly detected components range from 0.45-1.3 solar masses. Our orbits constrain these systems to a high astrometric precision, with median residuals to the orbital fit of 20-50 micro-arcseconds in most cases. For 7 of these systems we include newly obtained radial velocity data, which help us to identify the system configuration and to solve for masses of individual components in some cases. Although additional RV measurements are needed to break degeneracy in the mutual inclination, we find that the majority of these inner triples are not well-aligned with the wide binary orbit. This hints that higher mass triples are more misaligned compared to solar and lower mass triples, though a thorough study of survey biases is needed. We show that the ARMADA survey is extremely successful at uncovering previously unseen companions in binaries. This method will be used in upcoming papers to constrain companion demographics in intermediate mass binary systems down to the planetary mass regime.

astro-ph.SR↗

arXiv2021

Establishing $α$ Oph as a Prototype Rotator: Precision Orbit with new Keck, CHARA, and RV Observations

Alpha Ophiuchi (Rasalhague) is a nearby rapidly rotating A5IV star which has been imaged by infrared interferometry. $α$ Oph is also part of a known binary system, with a companion semi-major axis of $\sim$430 milli-arcseconds and high eccentricity of 0.92. The binary companion provides the unique opportunity to measure the dynamical mass to compare with the results of rapid rotator evolution models. The lack of data near periastron passage limited the precision of mass measurements in previous work. We add new interferometric data from the MIRC combiner at the CHARA Array as well as new Keck adaptive optics imaging data with NIRC2, including epochs taken near periastron passage. We also obtained new radial velocities of both components at Fairborn Observatory. Our updated combined orbit for the system drastically reduces the errors of the orbital elements, and allows for precise measurement of the primary star mass at the few percent level. Our resulting primary star mass of $2.20\pm0.06$ M$_{\odot}$ agrees well with predictions from imaging results, and matches evolution models with rotation when plotting on an HR diagram. However, to truly distinguish between non-rotating and rotating evolution models for this system we need $\sim$1\% errors on mass, which might be achieved once the distance is known to higher precision in future Gaia releases. We find that the secondary mass of $0.824\pm0.023$ M$_{\odot}$ is slightly under-luminous when compared to stellar evolution models. We show that $α$ Oph is a useful reference source for programs that need $\pm$1 milli-arcsecond astrometry.

astro-ph.SR↗

arXiv2021

Observations with the Differential Speckle Survey Instrument. X. Preliminary Orbits of K Dwarf Binaries and Other Stars

This paper details speckle observations of binary stars taken at the Lowell Discovery Telescope, the WIYN Telescope, and the Gemini telescopes between 2016 January and 2019 September. The observations taken at Gemini and Lowell were done with the Differential Speckle Survey Instrument (DSSI), and those done at WIYN were taken with the successor instrument to DSSI at that site, the NN-EXPLORE Exoplanet Star and Speckle Imager (NESSI). In total, we present 378 observations of 178 systems and we show that the uncertainty in the measurement precision for the combined data set is ~2 mas in separation, ~1-2 degrees in position angle depending on the separation, and $\sim$0.1 magnitudes in magnitude difference. Together with data already in the literature, these new results permit 25 visual orbits and one spectroscopic-visual orbit to be calculated for the first time. In the case of the spectroscopic-visual analysis, which is done on the trinary star HD 173093, we calculate masses with precision of better than 1% for all three stars in that system. Twenty-one of the visual orbits calculated have a K dwarf as the primary star; we add these to the known orbits of K dwarf primary stars and discuss the basic orbital properties of these stars at this stage. Although incomplete, the data that exist so far indicate that binaries with K dwarf primaries tend not to have low-eccentricity orbits at separations of one to a few tens of AU, that is, on solar-system scales.

astro-ph.SR↗

arXiv2020

ARMADA I: Triple Companions Detected in B-Type Binaries alpha Del and nu Gem

Ground-based optical long-baseline interferometry has the power to measure the orbits of close binary systems at ~10 micro-arcsecond precision. This precision makes it possible to detect "wobbles" in the binary motion due to the gravitational pull from additional short period companions. We started the ARrangement for Micro-Arcsecond Differential Astrometry (ARMADA) survey with the MIRC-X instrument at the CHARA array for the purpose of detecting giant planets and stellar companions orbiting individual stars in binary systems. We describe our observations for the survey, and introduce the wavelength calibration scheme that delivers precision at the tens of micro-arcseconds level for <0.2 arcsecond binaries. We test our instrument performance on a known triple system kappa Peg, and show that our survey is delivering a factor of 10 better precision than previous similar surveys. We present astrometric detections of tertiary components to two B-type binaries: a 30-day companion to alpha Del, and a 50-day companion to nu Gem. We also collected radial velocity data for alpha Del with the Tennessee State University Automated Spectroscopic Telescope at Fairborn Observatory. We are able to measure the orbits and masses of all three components in these systems. We find that the previously published RV orbit for the inner pair of nu Gem is not consistent with our visual orbit. The precision achieved for these orbits suggests that our ARMADA survey will be successful at discovering new compact triple systems to A/B-type binary systems, leading to better statistics of hierarchical system architectures and formation history.

astro-ph.SR↗

arXiv2020

Visual Orbits of Spectroscopic Binaries with the CHARA Array. III. HD 8374 and HD 24546

We present the visual orbits of two long period spectroscopic binary stars, HD 8374 and HD 24546, using interferometric observations acquired with the CHARA Array and the Palomar Testbed Interferometer. We also obtained new radial velocities from echelle spectra using the APO 3.5 m and Fairborn 2.0 m telescopes. By combining the visual and spectroscopic observations, we solve for the full, three-dimensional orbits and determine the stellar masses and distances to within 3% uncertainty. We then estimate the effective temperature and radius of each component star through Doppler tomography and spectral energy distribution analyses, in order to compare the observed stellar parameters to the predictions of stellar evolution models. For HD 8374, we find masses of M1 = 1.636 +/- 0.050 Msun and M2 = 1.587 +/- 0.049 Msun, radii of R1 = 1.84 +/- 0.05 Rsun and R2 = 1.66 +/- 0.12 Rsun, temperatures of Teff1 = 7280 +/- 110 K and Teff2 = 7280 +/- 120 K, and an estimated age of 1.0 Gyr. For HD 24546, we find masses of M1 = 1.434 +/- 0.014 Msun and M2 = 1.409 +/- 0.014 Msun, radii of R1 = 1.67 +/- 0.06 Rsun and R2 = 1.60 +/- 0.10 Rsun, temperatures of Teff1 = 6790 +/- 120 K and Teff2 = 6770 +/- 90 K, and an estimated age of 1.4 Gyr. HD 24546 is therefore too old to be a member of the Hyades cluster, despite its physical proximity to the group.

astro-ph.SR↗

arXiv2020

Observations of Binary Stars with the Differential Speckle Survey Instrument. IX. Observations of Known and Suspected Binaries, and a Partial Survey of Be Stars

We report 370 measures of 170 components of binary and multiple star systems, obtained from speckle imaging observations made with the Differential Speckle Survey Instrument at Lowell Observatory's Discovery Channel Telescope in 2015 through 2017. Of the systems studied, 147 are binary stars, 10 are seen as triple systems, and 1 quadruple system is measured. Seventy-six high-quality non-detections and fifteen newly resolved components are presented in our observations. The uncertainty in relative astrometry appears to be similar to our previous work at Lowell, namely linear measurement uncertainties of approximately 2 mas, and the relative photometry appears to be uncertain at the 0.1 to 0.15 magnitude level. Using these measures and those in the literature, we calculate six new visual orbits, including one for the Be star 66 Oph, and two combined spectroscopic-visual orbits. The latter two orbits, which are for HD 22451 (YSC 127) and HD 185501 (YSC 135), yield individual masses of the components at the level of 2 percent or better, and independent distance measures that in one case agrees with the value found in the Gaia DR2, and in the other disagrees at the 2-$σ$ level. We find that HD 22451 consists of an F6V+F7V pair with orbital period of $2401.1 \pm 3.2$ days and masses of $1.342 \pm 0.029$ and $1.236 \pm 0.026$ $ M_{\odot}$. For HD 185501, both stars are G5 dwarfs that orbit one another with a period of $433.94 \pm 0.15$ days, and the masses are $0.898 \pm 0.012$ and $0.876 \pm 0.012$ $ M_{\odot}$. We discuss the details of both the new discoveries and the orbit objects.

astro-ph.SR↗

arXiv2020

Absolute dimensions of the unevolved F-type eclipsing binary BT Vulpeculae

We report extensive differential V-band photometry and high-resolution spectroscopy for the 1.14 day, detached, double-lined eclipsing binary BT Vul (F0+F7). Our radial-velocity monitoring and light curve analysis lead to absolute masses and radii of M1 = 1.5439 +/- 0.0098 MSun and R1 = 1.536 +/- 0.018 RSun for the primary, and M2 = 1.2196 +/- 0.0080 MSun and R2 = 1.151 +/- 0.029 RSun for the secondary. The effective temperatures are 7270 +/- 150 K and 6260 +/- 180 K, respectively. Both stars are rapid rotators, and the orbit is circular. A comparison with stellar evolution models from the MIST series shows excellent agreement with these determinations, for a composition of [Fe/H] = +0.08 and an age of 350 Myr. The two components of BT Vul are very near the zero-age main sequence.

astro-ph.SR↗

arXiv2019

Absolute dimensions of the early F-type eclipsing binary V506 Ophiuchi

We report extensive differential V-band photometry and high-resolution spectroscopic observations of the early F-type, 1.06-day detached eclipsing binary V506 Oph. The observations along with times of minimum light from the literature are used to derive a very precise ephemeris and the physical properties for the components, with the absolute masses and radii being determined to 0.7% or better. The masses are 1.4153 +/- 0.0100 M(Sun) and 1.4023 +/- 0.0094 M(sun) for the primary and secondary, the radii are 1.725 +/- 0.010 R(Sun) and 1.692 +/- 0.012 R(Sun), and the effective temperatures 6840 +/- 150 K and 6780 +/- 110 K, respectively. The orbit is circular and the stars are rotating synchronously. The accuracy of the radii and temperatures is supported by the resulting distance estimate of 564 +/- 30 pc, in excellent agreement with the value implied by the trigonometric parallax listed in the Gaia/DR2 catalog. Current stellar evolution models from the MIST series for a composition of [Fe/H] = -0.04 match the properties of both stars in V506 Oph very well at an age of 1.83 Gyr, and indicate they are halfway through their core hydrogen-burning phase.

astro-ph.SR↗

arXiv2018

Separated Fringe Packet Observations with the CHARA Array III. The Very High Eccentricity Binary HR 7345

After an eleven year observing campaign, we present the combined visual{spectroscopic orbit of the formerly unremarkable bright star HR 7345 (HD 181655, HIP 94981, GJ 754.2). Using the Separated Fringe Packet (SFP) method with the CHARA Array, we were able to determine a difficult to complete orbital period of 331.609 +/- 0.004 days. The 11 month period causes the system to be hidden from interferometric view behind the Sun for 3 years at a time. Due to the high eccentricity orbit of about 90% of a year, after 2018 January the periastron phase will not be observable again until late 2021. Hindered by its extremely high eccentricity of 0.9322 +/- 0.0001, the double-lined spectroscopic phase of HR 7345 is observable for 15 days. Such a high eccentricity for HR 7345 places it among the most eccentric systems in catalogs of both visual and spectroscopic orbits. For this system we determine nearly identical component masses of 0.941 +/- 0.076 Msun and 0.926 +/- 0.075 Msun as well as an orbital parallax of 41.08 +/- 0.77 mas.

astro-ph.SR↗

arXiv2018

Precision Orbit of $δ$ Delphini and Prospects for Astrometric Detection of Exoplanets

Combining visual and spectroscopic orbits of binary stars leads to a determination of the full 3D orbit, individual masses, and distance to the system. We present a full analysis of the evolved binary system $δ$ Delphini using astrometric data from the MIRC and PAVO instruments on the CHARA long-baseline interferometer, 97 new spectra from the Fairborn Observatory, and 87 unpublished spectra from Lick Observatory. We determine the full set of orbital elements for $δ$ Del, along with masses of $1.78 \pm 0.07$ $M_{\odot}$ and $1.62 \pm 0.07$ $M_{\odot}$ for each component, and a distance of $63.61 \pm 0.89$ pc. These results are important in two contexts: for testing stellar evolution models and defining the detection capabilities for future planet searches. We find that the evolutionary state of this system is puzzling, as our measured flux ratios, radii, and masses imply a $\sim$ 200 Myr age difference between the components using standard stellar evolution models. Possible explanations for this age discrepancy include mass transfer scenarios with a now ejected tertiary companion. For individual measurements taken over a span of 2 years we achieve $<10$ $μ$-arcsecond precision on differential position with 10-minute observations. The high precision of our astrometric orbit suggests that exoplanet detection capabilities are within reach of MIRC at CHARA. We compute exoplanet detection limits around $δ$ Del, and conclude that if this precision is extended to wider systems we should be able to detect most exoplanets $>2$ M$_{J}$ on orbits $>0.75$ AU around individual components of hot binary stars via differential astrometry.

astro-ph.SR↗

arXiv2017

The quadruple-lined, doubly-eclipsing system V482 Persei

We report spectroscopic and differential photometric observations of the A-type system V482 Per that reveal it to be a rare hierarchical quadruple system containing two eclipsing binaries. One has the previously known orbital period of 2.4 days and a circular orbit, and the other a period of 6 days, a slightly eccentric orbit (e = 0.11), and shallow eclipses only 2.3% deep. The two binaries revolve around their common center of mass in a highly elongated orbit (e = 0.85) with a period of 16.67 yr. Radial velocities are measured for all components from our quadruple-lined spectra, and are combined with the light curves and with measurements of times of minimum light for the 2.4 day binary to solve for the elements of the inner and outer orbits simultaneously. The line-of-sight inclination angles of the three orbits are similar, suggesting they may be close to coplanar. The available observations appear to indicate that the 6 day binary experiences significant retrograde apsidal motion in the amount of about 60 degrees per century. We derive absolute masses for the four stars good to better than 1.5%, along with radii with formal errors of 1.1% and 3.5% for the 2.4 day binary and about 9% for the 6 day binary. A comparison of these and other physical properties with current stellar evolution models gives excellent agreement for a metallicity of [Fe/H] = -0.15 and an age of 360 Myr.

astro-ph.SR↗

arXiv2015

Absolute dimensions of the metallic-line eclipsing binary V501 Monocerotis

We report extensive high-resolution spectroscopic observations and V-band differential photometry of the slightly eccentric 7.02-day detached eclipsing binary V501 Mon (A6m+F0), which we use to determine its absolute dimensions to high precision (0.3% for the masses and 1.8% for the radii, or better). The absolute masses, radii, and temperatures are M(A) = 1.6455 +/- 0.0043 M(Sun), R(A) = 1.888 +/- 0.029 R(Sun), and T(A) = 7510 +/- 100 K for the primary, and M(B) = 1.4588 +/- 0.0025 M(Sun), R(B) = 1.592 +/- 0.028 R(Sun), and T(B) = 7000 +/- 90 K for the secondary. Apsidal motion has been detected, to which General Relativity contributes approximately 70%. The primary star is found to be a metallic-line A star. A detailed chemical analysis of the disentangled spectra yields abundances for more than a dozen elements in each star. Based on the secondary, the system metallicity is near solar: [Fe/H] = +0.01 +/- 0.06. Lithium is detected in the secondary but not in the primary. A comparison with current stellar evolution models shows a good match to the measured properties at an age of about 1.1 Gyr.

astro-ph.SR↗

arXiv2015

Detecting the Companions and Ellipsoidal Variations of RS CVn Primaries: II. omicron Draconis, a Candidate for Recent Low-Mass Companion Ingestion

To measure the stellar and orbital properties of the metal-poor RS CVn binary o Draconis (o Dra), we directly detect the companion using interferometric observations obtained with the Michigan InfraRed Combiner at Georgia State University's Center for High Angular Resolution Astronomy (CHARA) Array. The H-band flux ratio between the primary and secondary stars is the highest confirmed flux ratio (370 +/- 40) observed with long-baseline optical interferometry. These detections are combined with radial velocity data of both the primary and secondary stars, including new data obtained with the Tillinghast Reflector Echelle Spectrograph on the Tillinghast Reflector at the Fred Lawrence Whipple Observatory and the 2-m Tennessee State University Automated Spectroscopic Telescope at Fairborn Observatory. We determine an orbit from which we find model-independent masses and ages of the components (M_A = 1.35 +\- 0.05 M_Sun, M_B = 0.99 +\- 0.02 M_Sun, system age = 3.0 -\+ 0.5 Gyr). An average of a 23-year light curve of o Dra from the Tennessee State University Automated Photometric Telescope folded over the orbital period newly reveals eclipses and the quasi-sinusoidal signature of ellipsoidal variations. The modeled light curve for our system's stellar and orbital parameters confirm these ellipsoidal variations due to the primary star partially filling its Roche lobe potential, suggesting most of the photometric variations are not due to stellar activity (starspots). Measuring gravity darkening from the average light curve gives a best-fit of beta = 0.07 +\- 0.03, a value consistent with conventional theory for convective envelope stars. The primary star also exhibits an anomalously short rotation period, which, when taken with other system parameters, suggests the star likely engulfed a low-mass companion that had recently spun-up the star.

astro-ph.SR↗

arXiv2015

Detecting the Companions and Ellipsoidal Variations of RS CVn Primaries: I. sigma Geminorum

To measure the properties of both components of the RS CVn binary sigma Geminorum (sigma Gem), we directly detect the faint companion, measure the orbit, obtain model-independent masses and evolutionary histories, detect ellipsoidal variations of the primary caused by the gravity of the companion, and measure gravity darkening. We detect the companion with interferometric observations obtained with the Michigan InfraRed Combiner (MIRC) at Georgia State University's Center for High Angular Resolution Astronomy (CHARA) Array with a primary-to-secondary H-band flux ratio of 270+/-70. A radial velocity curve of the companion was obtained with spectra from the Tillinghast Reflector Echelle Spectrograph (TRES) on the 1.5-m Tillinghast Reflector at Fred Lawrence Whipple Observatory (FLWO). We additionally use new observations from the Tennessee State University Automated Spectroscopic and Photometric Telescopes (AST and APT, respectively). From our orbit, we determine model-independent masses of the components (M_1 = 1.28 +/- 0.07 M_Sun, M_2 = 0.73 +/- 0.03 M_Sun), and estimate a system age of 5 -/+ 1 Gyr. An average of the 27-year APT light curve of sigma Gem folded over the orbital period (P = 19.6027 +/- 0.0005 days) reveals a quasi-sinusoidal signature, which has previously been attributed to active longitudes 180 deg apart on the surface of sigma Gem. With the component masses, diameters, and orbit, we find that the predicted light curve for ellipsoidal variations due to the primary star partially filling its Roche lobe potential matches well with the observed average light curve, offering a compelling alternative explanation to the active longitudes hypothesis. Measuring gravity darkening from the light curve gives beta < 0.1, a value slightly lower than that expected from recent theory.

astro-ph.SR↗

arXiv2014

Absolute Properties of the Eclipsing Binary Star V501 Herculis

V501 Her is a well detached G3 eclipsing binary star with a period of 8.597687 days for which we have determined very accurate light and radial-velocity curves by using robotic telescopes. Results of these data indicate that the component stars have masses of 1.269 +/- 0.004 and 1.211 +/- 0.003 solar masses, radii of 2.001 +/- 0.003 and 1.511 +/- 0.003 solar radii, and temperatures of 5683 +/- 100K and 5720 +/- 100K, respectively. Comparison with the Yonsei-Yale series of evolutionary models results in good agreement at an age of about 5.1 Gyr for a somewhat metal rich composition. Those models indicate that the more massive, larger, slightly cooler star is just beyond core hydrogen exhaustion while the less massive, smaller, slightly hotter star has not quite reached core hydrogen exhaustion. The orbit is not yet circularized, and the components are rotating at or near their pseudosynchronous velocities. The distance to the system is 420 +/- 30 pc.

astro-ph.SR↗

arXiv2014

Absolute Properties of the Eclipsing Binary Star AP Andromedae

AP And is a well-detached F5 eclipsing binary star for which only a very limited amount of information was available before this publication. We have obtained very extensive measurements of the light curve (19097 differential V magnitude observations) and a radial velocity curve (83 spectroscopic observations) which allow us to fit orbits and determine the absolute properties of the components very accurately: masses of 1.277 +/- 0.004 and 1.251 +/- 0.004 solar masses, radii of 1.233 +/- 0.006 and 1.1953 +/- 0.005 solar radii, and temperatures of 6565 +/- 150 K and 6495 +/- 150 K. The distance to the system is about 400 +/- 30 pc. Comparison with the theoretical properties of the stellar evolutionary models of the Yonsei-Yale series of Yi et al. shows good agreement between the observations and the theory at an age of about 500 Myr and a slightly sub-solar metallicity.

astro-ph.SR↗