Parallaxes Of Stars Research Articles

VLBA Astrometry of the Fastest-spinning Magnetar Swift J1818.0−1607: A Large Trigonometric Distance and a Small Transverse Velocity

In addition to being the most magnetic objects in the known Universe, magnetars are the only objects observed to generate fast-radio-burst-like emissions. The formation mechanism of magnetars is still highly debated and may potentially be probed with the magnetar velocity distribution. We carried out a 3 yr long astrometric campaign on Swift J1818.0−1607, the fastest-spinning magnetar, using the Very Long Baseline Array. After applying the phase-calibrating 1D interpolation strategy, we obtained a small proper motion of 8.5 mas yr−1 mag and a parallax of 0.12 ± 0.02 mas (uncertainties at 1σ confidence throughout the Letter) for Swift J1818.0−1607. The latter is the second magnetar parallax and is among the smallest neutron star parallaxes ever determined. From the parallax, we derived the distance 9.4−1.6+2.0 kpc, which locates Swift J1818.0−1607 at the far side of the Galactic central region. Combined with the distance, the small proper motion leads to a transverse peculiar velocity v⊥=48−16+50 km s−1—a new lower limit to magnetar v ⊥. Incorporating previous v ⊥ estimates of seven other magnetars, we acquired v⊥=149−68+132 km s−1 for the sample of astrometrically studied magnetars, corresponding to the three-dimensional space velocity ∼190−87+168 km s−1, smaller than the average level of young pulsars. Additionally, we found that the magnetar velocity sample does not follow the unimodal young pulsar velocity distribution reported by Hobbs et al. at >2σ confidence, while loosely agreeing with more recent bimodal young pulsar velocity distributions derived from relatively small samples of quality astrometric determinations.

The Incomparable Monsignor: Francesco Bianchini’s world of science, history, and court intrigue by John L. Heilbron

Reviewed by: The Incomparable Monsignor: Francesco Bianchini’s world of science, history, and court intrigue by John L. Heilbron Christopher M. Graney The Incomparable Monsignor: Francesco Bianchini’s world of science, history, and court intrigue. By John L. Heilbron. (Oxford: Oxford University Press. 2022. Pp. vi, 327; 16 color plates. $27.95 hardbound. ISBN: 9780192856654.) Francesco Bianchini (1662–1729) was Superman. “Was there nothing Monsignor Bianchini could not do better than anyone else?” (p. 227) Apparently not. He did archaeology, history, diplomacy, spy craft, engineering, astronomy, and more. J. L. Heilbron has brought us church history through books on Galileo (2010) and on cathedrals as solar observatories (1999)—the latter provided many a Catholic apologist with a cherished quotation in its bold opening statement about the Church’s long support of science. The Incomparable is a readable, illustrated, informative addition to those books. Particularly appealing are The Incomparable’s sections about the meridian line (meridiana) that Bianchini built at Santa Maria degli Angeli church in Rome, and about Bianchini and Isaac Newton each reckoning a date for the sailing of Jason’s ship, [End Page 208] the Argos. The meridiana discussion shows Bianchini’s care for science and for making science interesting to others. He builds the meridiana to be both precise and beautiful. He works on its construction “night and day” (p. 94) for six months, thanks to his abilities (beyond those of ordinary men). He fits it with markers to indicate dates that interest important people. The Argos discussion shows how even supermen reflect their times (pp. 140–156). Newton was sure that all civilization derives from the ancient Jews; thus his dating efforts had to both fit that axiom and satisfy his keen mind. Bianchini had similar interests. Newton kept his to himself, but Heilbron thinks the English superman shared his secrets with the Italian (p. 151)—two keen minds (similarly keen, The Incomparable hints) undertaking an interdisciplinary labor that sought to pull archaeology, astronomy, ancient texts, and faith into a coherent narrative. Heilbron admires his Superman. Upon quoting Bianchini on how well-regulated minds following experts can approach truth, Heilbron marvels, “There spoke a senator of the Republic of Letters” (p. 205). Yet he burdens Superman with the old Kryptonite curse: Copernicus—of course. When the Kryptonite appears, the senator, the mind that thought with Newton, grows weak. He forgets truth. He capitulates to powerful people “unwilling to concede a lost game” (p. 13) who wield “soft arguments” (p. 11) against Copernicus. He accepts “the incomprehensible dogma” (p. 14) of the Church. Why? The Incomparable is a refreshing portrayal of a Catholic man of many talents, supported by and on good terms with his Pope and his Church, none of whom behave incomprehensibly—except for this. At times Heilbron does back off the trope, discussing Tycho Brahe and the parallax of stars and hinting at the complexity of the question of Earth’s motion and the evolving science of Bianchini’s lifetime that all might have made the game seem less than lost. Still, the index of The Incomparable has an entry for “spitoons” but none for “stars,” where lay the hard scientific arguments involved in that complexity. Heilbron treats Argos dating with more sympathy than Bianchini’s (supposed) Kryptonian flaw. The Incomparable’s own Kryptonite is its editing. There are technical errors that should have been caught, most obviously in the description of the meridiana (p. 92): Polaris in AD 2100 is closest to the celestial pole, not farthest; this scrambles at least a paragraph. There are also figures that contain letters indicating details, to which Heilbron often refers at length. The figures are small; the letters are nearly invisible. Some, such as Fig. 23, I could make use of, thanks to my large magnifying glass. Others, such as Figs. 30 and 31, defeated even the magnifier. There are no figures at all of Bianchini’s drawings of Venus, despite much discussion of those drawings. These hurt multiple paragraphs. The overall hurt to the book is not too great, however. Read The Incomparable—with a microscope, and a little skepticism, at hand. [End Page 209] Christopher M. Graney Vatican Observatory Copyright © 2023 The Catholic University...

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

The classical Cepheid η Aql was not included in past Leavitt Law work because of a presumed complicating orbit due to a known B9.8V companion. To determine the orbit of η Aql B, we analyze a significant number of radial velocity (RV) measurements from eight sources. With these we establish the RV variation due to Cepheid pulsation, using a model with 12 Fourier coefficients, 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 a 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 ζ Gem in parallel, deriving values for its parallax and proper motion consistent with Gaia EDR3, and consistent with the Benedict 2007 Leavitt Law. In an effort to further characterize η Aql B, we hypothesize that η 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 η Aql B. Ascribing photocenter motion to the photometric variation of the Cepheid, η Aql A, yields a plausible separation that is consistent with a long period and explains the lack of RV variation. None of these approaches yields an unassailable characterization of the η Aql A–B system.

Membership and age determination of M67 open cluster using GAIA EDR3 data

We present our study on the membership and age determination of M67 (NGC 2682), one of the oldest open clusters known to date. Proper motions and parallax of stars collected in the Gaia Early Data Release 3 are used to derive the cluster members by employing the Hierarchical Density-Based Spatial Clustering of Applications with Noise algorithm, which is further improved upon using a Gaussian Mixture Model. We calculate the position of the cluster centre and the parallax to be α = 08h51m24s±1m33s, δ = 11°49’12"±0°22’48" and 1.1497±0.06 mas respectively. The proper motion of the cluster is obtained to be μa = −10.96 ± 0.20 mas/yr and μs = −2.90 ± 0.19 mas/yr. Subsequently, we perform an isochrone fitting to the Color-Magnitude Diagram (CMD) of M67 source members by using the Automated Stellar Cluster Analysis tool (ASteCA). Our findings estimate the log age, metallicity (z), reddening (EB–V ), and distance modulus (m – M)0 to be 9.630 ± 0.033 log-years, 0.01865 ± 0.001, 0.037 ± 0.008, and 9.409 ± 0.031 respectively.

Gaia EDR3 view on galactic globular clusters

ABSTRACT We use the data from Gaia Early Data Release 3 (EDR3) to study the kinematic properties of Milky Way globular clusters. We measure the mean parallaxes and proper motions (PM) for 170 clusters, determine the PM dispersion profiles for more than 100 clusters, uncover rotation signatures in more than 20 objects, and find evidence for radial or tangential PM anisotropy in a dozen richest clusters. At the same time, we use the selection of cluster members to explore the reliability and limitations of the Gaia catalogue itself. We find that the formal uncertainties on parallax and PM are underestimated by $10{-}20{{\ \rm per\ cent}}$ in dense central regions even for stars that pass numerous quality filters. We explore the spatial covariance function of systematic errors, and determine a lower limit on the uncertainty of average parallaxes and PM at the level 0.01 mas and 0.025 mas yr$^{-1}$ , respectively. Finally, a comparison of mean parallaxes of clusters with distances from various literature sources suggests that the parallaxes for stars with $G>13$ (after applying the zero-point correction suggested by Lindegren et al.) are overestimated by $\sim 0.01\pm 0.003$ mas. Despite these caveats, the quality of Gaia astrometry has been significantly improved in EDR3 and provides valuable insights into the properties of star clusters.

Achievements of Space Astrometry

Astrometry is the basis for astronomical observations and measurements of coordinates and time. Its main task is to implement a reference frame—the one mentioned in Newton’s first law. Since ancient times, astronomers have created star catalogs for this purpose. Work on them led to the discovery of the precession and nutation of the Earth’s axis, proper motions and parallaxes of stars, and the orbital motion of binary stars. The modern International Celestial Reference Frame (ICRF) is based on observations in the radio and optical range of very distant objects—quasars. It is to them that the GPS or GLONASS system is tied in the navigation device. The 21st century, with its computational capabilities, has led to the creation of star catalogs of unprecedented power, containing over a billion objects. However, the main breakthrough, even a revolution in astrometry, has happened in space observations. Two spacecraft have already created star catalogs of fantastic accuracy, which makes it possible to approach the solution of problems even the setting of which was unthinkable a few years ago. This article is dedicated to an overview of the achievements of astrometry over the past two millennia, massive star catalogs, and space astrometric projects.

A Gaia view of the two OB associations Cygnus OB2 and Carina OB1: the signature of their formation process

ABSTRACT OB associations are the prime star-forming sites in galaxies. However, the detailed formation process of such stellar systems still remains a mystery. In this context, identifying the presence of substructures may help in tracing the footprints of their formation process. Here, we present a kinematic study of the two massive OB associations Cygnus OB2 and Carina OB1 using the precise astrometry from the Gaia Data Release 2 and radial velocities. From the parallaxes of stars, these OB associations are confirmed to be genuine stellar systems. Both Cygnus OB2 and Carina OB1 are composed of a few dense clusters and a halo which have different kinematic properties: the clusters occupy regions of 5–8 parsecs in diameter and display small dispersions in proper motion, while the haloes spread over tens of parsecs with two to three times larger dispersions in proper motion. This is reminiscent of the so-called line width–size relation of molecular clouds related to turbulence. Considering that the kinematics and structural features were inherited from those of their natal clouds would then imply that the formation of OB associations may result from structure formation driven by supersonic turbulence, rather than from the dynamical evolution of individual embedded clusters.

Comparison of Gaia DR2 Parallaxes of Stars with VLBI Astrometry

Abstract We compare the parallaxes of stars from VLBI astrometry in the literature to those in the Gaia DR2 catalog. Our full sample contains young stellar objects, evolved AGB stars, pulsars, and other radio stars. Excluding AGB stars, which show significant discrepancies between Gaia and VLBI parallaxes, and stars in binary systems, we obtain an average, systematic, parallax offset of −75 ± 29 μas for Gaia DR2, consistent with their estimate of a parallax zero-point between −100 and 0 μas.

The Sejong Open cluster Survey (SOS) VI. A small star-forming region in the high Galactic latitude molecular cloud MBM 110

We present optical photometric, spectroscopic data for the stars in the high Galactic latitude molecular cloud MBM 110. For the complete membership selection of MBM 110, we also analyze WISE mid-infrared data and Gaia astrometric data. Membership of individual stars is critically evaluated using the data mentioned above. The Gaia parallax of stars in MBM 110 is 2.667 +/- 0.095 mas (d = 375 +/- 13 pc), which confirms that MBM 110 is a small star-forming region in the Orion-Eridanus superbubble. The age of MBM 110 is between 1.9 Myr and 3.1 Myr depending on the adopted pre-main sequence evolution model. The total stellar mass of MBM 110 is between 16 M_sun (members only) and 23 M_sun (including probable members). The star formation efficiency is estimated to be about 1.4%. We discuss the importance of such small star formation regions in the context of the global star formation rate and suggest that a galaxy's star formation rate calculated from the Halpha luminosity may underestimate the actual star formation rate. We also confirm a young brown dwarf member based on photometry, spectroscopy, and astrometry.

First cosmological results using Type Ia supernovae from the Dark Energy Survey: measurement of the Hubble constant

ABSTRACT We present an improved measurement of the Hubble constant (H0) using the ‘inverse distance ladder’ method, which adds the information from 207 Type Ia supernovae (SNe Ia) from the Dark Energy Survey (DES) at redshift 0.018 < z < 0.85 to existing distance measurements of 122 low-redshift (z < 0.07) SNe Ia (Low-z) and measurements of Baryon Acoustic Oscillations (BAOs). Whereas traditional measurements of H0 with SNe Ia use a distance ladder of parallax and Cepheid variable stars, the inverse distance ladder relies on absolute distance measurements from the BAOs to calibrate the intrinsic magnitude of the SNe Ia. We find H0 = 67.8 ± 1.3 km s−1 Mpc−1 (statistical and systematic uncertainties, 68 per cent confidence). Our measurement makes minimal assumptions about the underlying cosmological model, and our analysis was blinded to reduce confirmation bias. We examine possible systematic uncertainties and all are below the statistical uncertainties. Our H0 value is consistent with estimates derived from the Cosmic Microwave Background assuming a ΛCDM universe.

The dynamical matter density in the solar neighbourhood inferred from Gaia DR1

We determine the total dynamical density in the solar neighbourhood using the Tycho-Gaia Astrometric Solution (TGAS) catalogue. Astrometric measurements of proper motion and parallax of stars inform us of both the stellar number density distribution and the velocity distribution of stars close to the plane. Assuming equilibrium, these distributions are interrelated through the local dynamical density. For the first time, we do a full joint fit of the velocity and stellar number density distributions while accounting for the astrometric error of individual stars, in the framework of Bayesian Hierarchical Modelling. We use a sample of stars whose distance extends to approximately 160 pc from the Sun. We find a local matter density of $\rho_0 = 0.119^{+0.015}_{-0.012}~M_\odot$pc$^{-3}$, where the result is presented as the median to the posterior distribution, plus/minus its 16th and 84th percentiles. We find the Sun's position above the Galactic plane to be $z_\odot = 15.3^{+2.24}_{-2.16}$ pc, and the Sun's velocity perpendicular to the Galactic plane to be $W_\odot = 7.19^{+0.18}_{-0.18}$ km/s.

Dating the Tidal Disruption of Globular Clusters with GAIA Data on Their Stellar Streams

Abstract The Gaia mission promises to deliver precision astrometry at an unprecedented level, heralding a new era for discerning the kinematic and spatial coordinates of stars in our Galaxy. Here, we present a new technique for estimating the age of tidally disrupted globular cluster streams using the proper motions and parallaxes of tracer stars. We evolve the collisional dynamics of globular clusters within the evolving potential of a Milky Way-like halo extracted from a cosmological ΛCDM simulation and analyze the resultant streams as they would be observed by Gaia. The simulations sample a variety of globular cluster orbits, and account for stellar evolution and the gravitational influence of the disk of the Milky Way. We show that a characteristic timescale, obtained from the dispersion of the proper motions and parallaxes of stars within the stream, is a good indicator for the time elapsed since the stream has been freely expanding away due to the tidal disruption of the globular cluster. This timescale, in turn, places a lower limit on the age of the cluster. The age can be deduced from astrometry using a modest number of stars, with the error on this estimate depending on the proximity of the stream and the number of tracer stars used.

Kinematics of Stars from the TGAS (Gaia DR1) Catalogue

Based on the stellar proper motions of the TGAS (Gaia DR1) catalogue, we have analyzed the velocity field of main-sequence stars and red giants from the TGAS catalogue with heliocentric distances up to 1.5 kpc. We have obtained four variants of kinematic parameters corresponding to different methods of calculating the distances from the parallaxes of stars measured with large relative errors. We have established that within the Ogorodnikov–Milne model changing the variant of distances affects significantly only the solar velocity components relative to the chosen centroid of stars, provided that the solution is obtained in narrow ranges of distances (0.1 kpc). The estimates of all the remaining kinematic parameters change little. This allows the Oort coefficients and related Galactic rotation parameters as well as all the remaining Ogorodnikov–Milne model parameters (except for the solar terms) to be reliably estimated irrespective of the parallax measurement accuracy. The main results obtained from main-sequence stars in the range of distances from 0.1 to 1.5 kpc are: A = 16.29 ± 0.06 km s−1 kpc−1, B = −11.90 ± 0.05 km s−1 kpc−1, C = −2.99 ± 0.06 km s−1 kpc−1, K = −4.04 ± 0.16 km s−1 kpc−1, and the Galactic rotation period P = 217.41 ± 0.60 Myr. The analogous results obtained from red giants in the range from 0.2 to 1.6 kpc are: the Oort constants A = 13.32 ± 0.09 km s−1 kpc−1, B = −12.71 ± 0.06 km s−1 kpc−1, C = −2.04 ± 0.08 km s−1 kpc−1, K = −2.72 ± 0.19 km s−1 kpc−1, and the Galactic rotation period P = 236.03 ± 0.98 Myr. The Galactic rotation velocity gradient along the radius vector (the slope of the Galactic rotation curve) is −4.32 ± 0.08 km s−1 kpc−1 for main-sequence stars and −0.61 ± 0.11 km s−1 kpc−1 for red giants. This suggests that the Galactic rotation velocity determined from main-sequence stars decreases with increasing distance from the Galactic center faster than it does for red giants.

Testing Metal-poor Stellar Models and Isochrones with HST Parallaxes of Metal-poor Stars

Abstract Hubble Space Telescope (HST) fine guidance sensor observations were used to obtain parallaxes of eight metal-poor ([Fe/H] < −1.4) stars. The parallaxes of these stars determined by the new Hipparcos reduction average 17% accuracy, in contrast to our new HST parallaxes, which average 1% accuracy and have errors on the individual parallaxes ranging from 85 to 144 μas. These parallax data were combined with HST Advanced Camera for Surveys photometry in the F606W and F814W filters to obtain the absolute magnitudes of the stars with an accuracy of 0.02–0.03 mag. Six of these stars are on the main sequence (MS) (with −2.7 < [Fe/H] < −1.8) and are suitable for testing metal-poor stellar evolution models and determining the distances to metal-poor globular clusters (GCs). Using the abundances obtained by O’Malley et al., we find that standard stellar models using the VandenBerg & Clem color transformation do a reasonable job of matching five of the MS stars, with HD 54639 ([Fe/H] = −2.5) being anomalous in its location in the color–magnitude diagram. Stellar models and isochrones were generated using a Monte Carlo analysis to take into account uncertainties in the models. Isochrones that fit the parallax stars were used to determine the distances and ages of nine GCs (with −2.4 ≤ [Fe/H] ≤ −1.9). Averaging together the age of all nine clusters led to an absolute age of the oldest, most metal-poor GCs of 12.7 ± 1.0 Gyr, where the quoted uncertainty takes into account the known uncertainties in the stellar models and isochrones, along with the uncertainty in the distance and reddening of the clusters.

Seeing Earth's Orbit in the Stars: Parallax and Aberration

During the 17th century the idea of an orbiting and rotating Earth became increasingly popular, but opponents of this view continued to point out that the theory had observable consequences that had never, in fact, been observed.1 Why, for instance, had astronomers failed to detect the annual parallax of the stars that must occur if Earth orbits the Sun? To address this problem, astronomers of the 17th and 18th centuries sought to measure the annual parallax of stars using telescopes. None of them succeeded. Annual stellar parallax was not successfully measured until 1838, when Friedrich Bessel detected the parallax of the star 61 Cygni.2 But the early failures to detect annual stellar parallax led to the discovery of a new (and entirely unexpected) phenomenon: the aberration of starlight. This paper recounts the story of the discovery of stellar aberration. It is accompanied by a set of activities and computer simulations that allow students to explore this fascinating historical episode and learn important lessons about the nature of science.3

A kinematic study and membership analysis of the Lupus star-forming region

This paper is dedicated to investigating the kinematic properties of the Lupus moving group of young stars with the primary objective of deriving individual parallaxes for each group member. We identify those stars in the Lupus star-forming region that define the comoving association of young stars by utilizing our new and improved convergent point search method that allows us to derive the precise position of the convergent point of the comoving association from the stars' proper motions. We used published proper motion catalogs and searched the literature for radial velocities, which are needed to compute individual parallaxes. We supplemented the radial velocity data with new measurements from spectroscopic observations performed with the FEROS spectrograph mounted on the MPG/ESO 2.2m telescope at La Silla. We identify a comoving group with 109 pre-main sequence stars and candidates that define the kinematic properties of the Lupus low-mass star-forming region. We derive individual parallaxes for stars with known radial velocity and tentative parallaxes for the remaining group members by assuming that all stars share the same space motion. The convergent point method, combined with the k-NN algorithm, makes it possible to distinguish the Lupus and Upper Centaurus Lupus stars from the adjacent Scorpius-Centaurus association. We find significant depth effects in this region and show that the classical T Tauri stars, located in the close vicinity of the Lupus molecular clouds, form a background population, while the weak-emission line T Tauri stars are dispersed not only in angular extent but also in depth. The newly derived individual parallaxes will be used in a forthcoming paper to refine the masses and ages of Lupus T Tauri stars, with the aim of better constraining the lifetimes of their circumstellar, protoplanetary disks.

THE CHARA ARRAY ANGULAR DIAMETER OF HR 8799 FAVORS PLANETARY MASSES FOR ITS IMAGED COMPANIONS

HR 8799 is an hF0 mA5 gamma Doradus, lambda Bootis, Vega-type star best known for hosting four directly imaged candidate planetary companions. Using the CHARA Array interferometer, we measure HR 8799's limb-darkened angular diameter to be 0.342 +/- 0.008 mas; this is the smallest interferometrically measured stellar diameter to date, with an error of only 2%. By combining our measurement with the star's parallax and photometry from the literature, we greatly improve upon previous estimates of its fundamental parameters, including stellar radius (1.44 +/- 0.06 R_Sun), effective temperature (7193 +/- 87 K, consistent with F0), luminosity (5.05 +/- 0.29 L_Sun), and the extent of the habitable zone (1.62 AU to 3.32 AU). These improved stellar properties permit much more precise comparisons with stellar evolutionary models, from which a mass and age can be determined, once the metallicity of the star is known. Considering the observational properties of other lambda Bootis stars and the indirect evidence for youth of HR 8799, we argue that the internal abundance, and what we refer to as the effective abundance, is most likely near-solar. Finally, using the Yonsei-Yale evolutionary models with uniformly scaled solar-like abundances, we estimate HR 8799's mass and age considering two possibilities: 1.516 +0.038/-0.024 M_Sun and 33 +7/-13 Myr if the star is contracting toward the zero age main-sequence or 1.513 +0.023/-0.024 M_Sun and 90 +381/-50 Myr if it is expanding from it. This improved estimate of HR 8799's age with realistic uncertainties provides the best constraints to date on the masses of its orbiting companions, and strongly suggests they are indeed planets. They nevertheless all appear to orbit well outside the habitable zone of this young star.

ERRATUM: “CONFIRMING FUNDAMENTAL PROPERTIES OF THE EXOPLANET HOST STAR ϵ ERIDANI USING THE NAVY OPTICAL INTERFEROMETER” (2012, ApJ, 744, 138B)

We measured the angular diameter of the exoplanet host star epsilon Eridani using the Navy Optical Interferometer. We determined its physical radius, effective temperature, and mass by combining our measurement with the star's parallax, photometry from the literature, and the Yonsei-Yale isochrones (Yi et al. 2001), respectively. We used the resulting stellar mass of 0.82 +/- 0.05 M_Sun plus the mass function from Benedict et al. (2006) to calculate the planet's mass, which is 1.53 +/- 0.22 M_Jupiter. Using our new effective temperature, we also estimated the extent of the habitable zone for the system.

CONFIRMING FUNDAMENTAL PROPERTIES OF THE EXOPLANET HOST STAR ϵ ERIDANI USING THE NAVY OPTICAL INTERFEROMETER

We measured the angular diameter of the exoplanet host star Eridani using the Navy Optical Interferometer. We determined its physical radius, effective temperature, and mass by combining our measurement with the star's parallax, photometry from the literature, and the Yonsei-Yale isochrones, respectively. We used the resulting stellar mass of 0.82 ± 0.05 M ☉ plus the mass function from Benedict et al. to calculate the planet's mass, which is 1.53 ± 0.22 M Jupiter. Using our new effective temperature, we also estimated the extent of the habitable zone for the system.

FUNDAMENTAL PARAMETERS OF THE EXOPLANET HOST K GIANT STAR ι DRACONIS FROM THE CHARA ARRAY

We measured the angular diameter of the exoplanet host star iota Dra with Georgia State University's Center for High Angular Resolution Astronomy (CHARA) Array interferometer, and, using the star's parallax and photometry from the literature, calculated its physical radius and effective temperature. We then combined our results with stellar oscillation frequencies from Zechmeister et al. (2008) and orbital elements from Kane et al. (2010) to determine the masses for the star and exoplanet. Our value for the central star's mass is 1.82 +/- 0.23 M_Sun, which means the exoplanet's minimum mass is 12.6 +/- 1.1 M_Jupiter. Using our new effective temperature, we recalculated the habitable zone for the system, though it is well outside the star-planet separation.