Hipparcos Distance Research Articles

Dynamical masses for the nearest brown dwarf binary: ε Indi Ba,b

Binary brown dwarfs are important because their dynamical masses can be determined in a model-independent way. If a main sequence star is also involved, the age and metallicity for the system can be determined, making it possible to break the sub-stellar mass-age degeneracy. The most suitable benchmark system for intermediate age T dwarfs is ε Indi Ba,b, two T dwarfs (spectral types T1 and T6; McCaughrean et al. (2004)) orbiting a K4.5V star, ε Indi A, at a projected separation of 1460AU. At a distance of 3.6224pc (HIPPARCOS distance to ε Indi A; van Leeuwen (2007)), these are the closest brown dwarfs to the Earth, and thus both components are bright and the system is well-resolved. The system has been monitored astrometrically with NACO and FORS2 on the VLT since June 2004 and August 2005, respectively, in order to determine the system and individual masses independent of evolutionary models. We have obtained a preliminary system mass of 121±1MJup. We have also analysed optical/near-IR spectra (0.6-5.0μm at a resolution up to R~5000; King et al. (2009)) allowing us to determine bolometric luminosities, compare and calibrate evolutionary and atmospheric models of T dwarfs at an age of 4-8Gyr.

The galactic unclassified B[e] star HD 50138

The observed spectral variation of HD 50138 has led different authors to classify it in a very wide range of spectral types and luminosity classes (from B5 to A0 and III to Ia) and at different evolutionary stages as either HAeBe star or classical Be. Aims: Based on new high-resolution optical spectroscopic data from 1999 and 2007 associated to a photometric analysis, the aim of this work is to provide a deep spectroscopic description and a new set of parameters for this unclassified southern B[e] star and its interstellar extinction. Methods: From our high-resolution optical spectroscopic data separated by 8 years, we perform a detailed spectral description, presenting the variations seen and discussing their possible origin. We derive the interstellar extinction to HD 50138 by taking the influences of the circumstellar matter in the form of dust and an ionized disk into account. Based on photometric data from the literature and the new Hipparcos distance, we obtain a revised set of parameters for HD 50138. Results: Because of the spectral changes, we tentatively suggest that a new shell phase could have taken place prior to our observations in 2007. We find a color excess value of E(B-V) = 0.08 mag, and from the photometric analysis, we suggest that HD 50138 is a B6-7 III-V star. A discussion of the different evolutionary scenarios is also provided.

2MASS 22344161+4041387AB: A WIDE, YOUNG, ACCRETING, LOW-MASS BINARY IN THE LkHα233 GROUP

We report the discovery of a young, 016 binary, 2M2234+4041AB, found as the result of a Keck laser guide star adaptive optics imaging survey of young field ultracool dwarfs. Spatially resolved near-infrared photometry and spectroscopy indicate that the luminosity and temperature ratios of the system are near unity. From optical and near-infrared spectroscopy, we determine a composite spectral type of M6 for the system. Gravity-sensitive spectral features in the spectra of 2M2234+4041AB are best matched to those of young objects (∼1 Myr old). A comparison of the Teff and age of 2M2234+4041AB to evolutionary models indicates that the mass of each component is 0.10+0.075−0.04 M☉. Emission lines of Hα in the composite optical spectrum of the system and Brγ in spatially resolved near-IR spectra of the two components indicate that the system is actively accreting. Both components of the system have IR excesses, indicating that they both harbor circumstellar disks. Though 2M2234+4041AB was originally identified as a young field dwarf, it lies 15 from the well-studied Herbig Ae/Be star, LkHα233. The distance to LkHα233 is typically assumed to be 880 pc. It is unlikely that 2M2234+4041AB could be this distant, as it would then be more luminous than any known Taurus objects of similar spectral type. We re-evaluate the distance to the LkHα233 group and find a value of 325+72−50 pc, based on the Hipparcos distance to a nearby B3-type group member (HD 213976). 2M2234+4041AB is the first low-mass star to be potentially associated with the LkHα233 group. At a distance of 325 pc, its projected physical separation is 51 AU, making it one of the growing number of wide, low-mass binaries found in young star-forming regions.

Interferometric Studies of the Extreme Binary ∊ Aurigae: Pre-Eclipse Observations

We report new and archival K-band interferometric uniform disk diameters obtained with the Palomar Testbed Interferometer for the eclipsing binary star $\epsilon$ Aurigae, in advance of the start of its eclipse in 2009. The observations were inteded to test whether low amplitude variations in the system are connected with the F supergiant star (primary), or with the intersystem material connecting the star with the enormous dark disk (secondary) inferred to cause the eclipses. Cepheid-like radial pulsations of the F star are not detected, nor do we find evidence for proposed 6% per decade shrinkage of the F star. The measured 2.27 +/- 0.11 milli-arcsecond K band diameter is consistent with a 300 times solar radius F supergiant star at the Hipparcos distance of 625 pc. These results provide an improved context for observations during the 2009-2011 eclipse.

Diameter and photospheric structures of Canopus from AMBER/VLTI interferometry

Context. Direct measurements of fundamental parameters and photospheric structures of post-main-sequence intermediate-mass stars are required for a deeper understanding of their evolution. Aims. Based on near-IR long-baseline interferometry we aim to resolve the stellar surface of the F0 supergiant star Canopus, and to precisely measure its angular diameter and related physical parameters. Methods. We used the AMBER/VLTI instrument to record interferometric data on Canopus: visibilities and closure phases in the H and K bands with a spectral resolution of 35. The available baselines (’ 60 110 m) and the high quality of the AMBER/VLTI observations allowed us to measure fringe visibilities as far as in the third visibility lobe. Results. We determined an angular diameter of = = 6:93 0:15 mas by adopting a linearly limb-darkened disk model. From this angular diameter and Hipparcos distance we derived a stellar radius R = 71:4 4:0R . Depending on bolometric fluxes existing in the literature, the measured = provides two estimates of the e ective temperature: Te = 7284 107 K and Te = 7582 252 K. Conclusions. In addition to providing the most precise angular diameter obtained to date, the AMBER interferometric data point towards additional photospheric structures on Canopus beyond the limb-darkened model alone. A promising explanation for such surface structures is the presence of convection cells. We checked such a hypothesis using first order star-cell models and concluded that the AMBER observations are compatible with the presence of surface convective structures. This direct detection of convective cells on Canopus from interferometry can provide strong constraints to radiation-hydrodynamics models of photospheres of F-type supergiants.

Spectroscopic distances of 28 nearby star candidates

Aims. Twenty eight hitherto neglected candidates for the Catalogue of Nearby Stars (CNS) were investigated to verify their classification and to improve their distance estimates. All targets had at least a preliminary status of being nearby dwarf stars based on their large proper motions and relatively faint magnitudes. Better photometric and/or spectroscopic distances were required for selecting stars for further trigonometric parallax measurements. Methods. Low-resolution spectra were obtained with NASPEC at the Tautenburg 2 m telescope and with CAFOS at the Calar Alto 2.2 m telescope. The spectral types of M-type stars were determined by direct comparison of the target’s spectra with those of comparison stars of known spectral types observed with the same instrument. The classification of earlier types was performed based on comparison with published spectral libraries. Results. For most of the target stars reliable spectral types could be determined and in combination with 2MASS photometry new improved distance estimates became available. The majority were classified as M dwarfs including 11 stars within 25 pc. The fainter component of LDS 1365, previously thought to form a nearby common proper motion pair, is according to our results an unrelated high-velocity background star. For several other nearby common proper motion pairs our distance estimates of the fainter components are in good agreement with Hipparcos distances of the brighter components. The three stars in our sample that were previously thought to be white dwarfs (GJ 2091, GJ 2094, GJ 2098) turned out to be more distant high-velocity F- to K-type (sub)dwarfs. For the star with the largest tangential velocity (GJ 2091; v tan > 500 km s −1 ) we have additional evidence for its probable Galactic halo membership from a measured large radial velocity of 266 ± 25 km s −1 and from its UBV photometry indicating a low metallicity.

Synthetic Spectrum Constraints on a Model of the Cataclysmic Variable QU Carinae

Neither standard model SEDs nor truncated standard model SEDs fit observed spectra of QU Carinae with acceptable accuracy over the range 900-3000 A. Nonstandard model SEDs fit the observation set accurately. The nonstandard accretion disk models have a hot region extending from the white dwarf to -->R = 1.36RWD, a narrow intermediate-temperature annulus, and an isothermal remainder to the tidal cutoff boundary. The models include a range of $d{M}$ --> values between -->1.0 × 10−7 and -->1.0 × 10−6 M☉ yr−1 and limiting values of MWD between 0.6 and 1.2 M☉. A solution with -->MWD = 1.2 M☉ is consistent with an empirical mass-period relation. The set of models agree on a limited range of possible isothermal region Teff values between 14,000 and 18,000 K. The model-to-model residuals are so similar that it is not possible to choose a best model. The Hipparcos distance, 610 pc, is representative of the model results. The orbital inclination is between 40° and 60°.

Asiago eclipsing binaries program

The orbit and physical parameters of the previously unsolved double-lined eclipsing binary V570 Per, discovered by the Hipparcos satellite, were derived using high-resolution Echelle spectroscopy and B,V photoelectric photometry. The metallicity from χ 2 analysis of the spectra is (M/H) =+ 0.02 ± 0.03, and reddening from interstellar NaI and KI absorption lines is EB−V = 0.023 ± 0.007. V570 Per is a well-detached system, with shallow eclipses (due to low orbital inclination) and no sign of chromospheric activity. The two components have masses of 1.449 ± 0.006 and 1.350 ± 0.006 Mand spectral types F3 and F5, respectively. They are both still within the main sequence band (T1 = 6842 ± 25 K, T2 = 6562 ± 25 K from χ 2 analysis, R1 = 1.523 ± 0.030, R2 = 1.388 ± 0.019 R� derived by forcing the orbital solution to conform to the spectroscopic light ratio) and are dynamically relaxed to co-rotation with the orbital motion (Vrot,1,2 sini = 40 and 36 (±1) km s −1 ). The distance to V570 Per obtained from the orbital solution is 123 ± 2p c, in excellent agreement with the revised Hipparcos distance of 123 ± 11 pc. The observed properties of V570 Per components were compared to available families of stellar evolutionary tracks and, in particular, to BaSTI models computed on purpose for exactly the observed masses and varied chemical compositions. This system is interesting since both components have their masses in the range where the efficiency of convective core overshooting has to decrease with the total mass as a consequence of the decreasing size of the convective core during the central H-burning stage. Our numerical simulations show that, in order to match all empirical constraints, a small but not null overshooting is required, with efficiencies of λOV = 0.14 and 0.11 for the 1.449 and 1.350 Mcomponents, respectively. This confirms the finding of Paper II on the similar system V505 Per. At the ≈0.8 Gyr age of the system, the element diffusion has reduced the surface metallicity of the models from the initial (M/H) =+ 0.17 to (M/H) =+ 0.02, in perfect agreement with the spectroscopically derived (M/H) =+ 0.02 ± 0.03 value.

MAIN-SEQUENCE FITTING DISTANCE TO THE σ Ori CLUSTER

The σ Ori cluster is an unbound aggregate of a few hundred young, low-mass stars centered on the multiple system σ Ori. This cluster is of great interest because it is at an age when roughly half of the stars have lost their protoplanetary disks, and the cluster has a very large population of brown dwarfs. One of the largest sources of uncertainty in the properties of the cluster is that the distance is not well known. The directly measured Hipparcos distance to σ Ori AB is 350+120 –90 pc. On the other hand, the distance to the Orion OB1b subgroup (of which σ Ori is thought to be a member), 473 ± 40 pc, is far better determined, but it is an indirect estimate of the cluster's distance. Also, Orion OB1b may have a depth of 40 pc along our line of sight. We use main-sequence fitting to nine main-sequence cluster members to estimate a best-fit distance of 420 ± 30 pc, assuming a metallicity of –0.16 ± 0.11 or 444 pc assuming solar metallicity. A distance as close as 350 pc is inconsistent with the observed brightnesses of the cluster members. At the best-fit distance, the age of the cluster is 2-3 Myr.

The early-type semidetached binary system V716 Centaurus

New high-resolution spectra of V716 Cen revealed for the first time lines of the secondary component and its radial velocities. The simultaneous solution of the new radial velocity curves and the Hipparcos light curve yield the reliable absolute dimensions of this semidetached system. The masses for the primary and secondary are M 1 = 5.68 ± 0.07 M ⊙ and M 2 = 2.39 ± 0.05 M ⊙ , respectively, and the radii are R 1 = 4.08 ± 0.07 R ⊙ and R 2 = 3.36 ± 0.02 R ⊙ . We derive also effective temperatures of T eff1 = 15 500 ± 50 K and T eff2 = 9000 ± 80 K, and equatorial rotational velocities of u rot sin i = 137 ± 2 km s -1 and v rot sin i = 116 ± 7 km s -1 . These rotational velocities imply that the components rotate synchronously. The distance to the system is d = 339 ± 8 pc, in good agreement with the less accurate Hipparcos distance (337 ± 72 pc). The primary is underluminous and the secondary overluminous compared to normal main-sequence stars of the same mass. This implies that the secondary component of the semidetached system is in slow mass transferring stage after mass ratio reversal, although the Ha-line profiles do not show clear evidence for this.

Hipparcos distance estimates of the Ophiuchus and the Lupus cloud complexes

We combine extinction maps from the Two Micron All Sky Survey (2MASS) with Hipparcos and Tycho parallaxes to obtain reliable and high-precision estimates of the distance to the Ophiuchus and Lupus dark complexes. Our analysis, based on a rigorous maximumlikelihood approach, shows that the ρ-Ophiuchi cloud is located at (119 ± 6) pc and the Lupus complex is located at (155 ± 8) pc; in addition, we are able to put constraints on the thickness of the clouds and on their orientation on the sky (both these effects are not included in the error estimate quoted above). For Ophiuchus, we find some evidence that the streamers are closer to us than the core. The method applied in this paper is currently limited to nearby molecular clouds, but it will find many natural applications in the GAIA-era, when it will be possible to pin down the distance and three-dimensional structure of virtually every molecular cloud in the Galaxy.

Eclipsing Binary Solutions in Physical Units and Direct Distance Estimation

Opportunities for extraction of distances and temperatures from eclipsing binary light curves that are in standard flux units, as opposed to traditional arbitrary units, are examined. Benefits include (1) distance becomes an ordinary solution parameter with a standard error, (2) temperatures of both stars may be derivable in favorable circumstances, and (3) semidetached and overcontact binaries suffer no loss of distance accuracy, vis-a-vis well-detached binaries. Flux calibrations enter only for the observations, while theoretical fluxes are naturally in standard units, so confrontation of theory and observation is direct, and semiempirical quantities based on color-temperature relations are not needed. The monolithic process, called direct distance estimation (DDE), also saves time and effort by avoiding separate distance estimation steps and should lead to routine distance measurements for large numbers of eclipsing binaries (EBs). Discussions compare DDE with traditional EB distance estimation, which has been restricted to well detached binaries in most publications. Aspect dependence of spectroscopic or color temperature, as affected by tides and irradiation, is treated rigorously. A temperature-distance theorem that specifies requirements for finding temperatures and distance from EB light and velocity curves is checked by several kinds of simulations. Demonstration solutions are carried out for the overcontact binary AW UMa and the semidetached binary RZ Cnc, with discussions of temperature and distance results. Although AW UMa has many observational and structural oddities, its DDE and Hipparcos distances agree. Six DDE distances for RZ Cnc, done in several ways and for three photometric bands, fall well within the 1 σ range of its Hipparcos distance. Interactions among calibrative errors, parameter values, and fitting discrepancies are discussed, as is proper weighting.

Photometric study of the W UMa eclipsing binaries VW LMi and BX Dra

New ephemeris and the absolute parameters—masses, radii and luminosities—of the contact systems VW LMi and BX Dra have been obtained, by means of the analysis of the minima data available in the literature (for the determination of the ephemeris) and combining the previously published spectroscopic information and the results of the Wilson-Devinney method using photometric data (for the determination of the absolute parameters). The VW LMi O−C analysis confirms the multiplicity of the system detected previously from the spectroscopic data. Masses of the VW LMi contact system primary and secondary components are 1.67 ± 0.02M ⊙ and 0.70 ± 0.02M ⊙, respectively. The corresponding radii are 1.709 ± 0.007R ⊙ and 1.208 ± 0.006R ⊙, respectively. For the BX Dra contact system the masses are 2.19 ± 0.13M ⊙ and 0.63 ± 0.06M ⊙, and the radii, 2.13 ± 0.04R ⊙ and 1.26 ± 0.03R ⊙, for the primary and secondary, respectively. In both cases, the estimated luminosities seem to be slightly greater that the values derived from the Hipparcos distances.

A maximum-likelihood method for fitting colour–magnitude diagrams

We present a maximum-likelihood method for fitting two-dimensional model distributions to stellar data in colour–magnitude space. This allows one to include (for example) binary stars in an isochronal population. The method also allows one to derive formal uncertainties for fitted parameters, and assess the likelihood that a good fit has been found. We use the method to derive an age of 38.5+3.5−6.5 Myr and a true distance modulus of 7.79+0.11−0.05 mag from the V versus V−I diagram of NGC 2547 (the uncertainties are 67 per cent confidence limits, and the parameters are insensitive to the assumed binary fraction). These values are consistent with those previously determined from low-mass isochronal fitting, and are the first measurements to have statistically meaningful uncertainties. The age is also consistent with the lithium depletion age of NGC 2547, and the Hipparcos distance to the cluster is consistent with our value. The method appears to be quite general and could be applied to any N-dimensional data set, with uncertainties in each dimension. However, it is particularly useful when the data are sparse, in the sense that both the typical uncertainties for a data point and the size of structure in the function being fitted are small compared with the typical distance between data points. In this case binning the data will lose resolution, whilst the method presented here preserves it. Software implementing the methods described in this paper is available from http://www.astro.ex.ac.uk/people/timn/tau-squared/.

First ground-based photometry and light-curve analysis of the eccentric eclipsing binary V744 Cas

The first ground-based BVR photometric observations of the recently discovered eclipsing binary V744 Cas are presented. From these measurements, timings for two primary and one secondary minima have been calculated. The light curves of the system were analyzed by using the Wilson-Devinney program. The analysis shows that the system is detached with two similar components of spectral type A2V, and the orbit is eccentric (e = 0.0662 ± 0.0005). The longitude of the periastron (ω) was found significantly different for two different light curves (ours and that of Hipparcos), which is strongly suggestive of an apsidal motion with a period of about 425 ± 68 yr. This makes V744 Cas an important candidate for studies of apsidal motions. The first estimate of the absolute dimensions place the system close to the terminal age of the main sequence (TAMS) in the HR diagram. The distance from the spectroscopic parallax (d = 740 ± 10 pc) was found to be slightly larger than the Hipparcos distance of d = 610 ± 400 pc. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

HD 3651 B: the first directly imaged brown dwarf companion of an exoplanet host star

Abstract In the course of our ongoing multiplicity study of exoplanet host stars we detected a faint companion located at ∼43 arcsec (480 au physical projected separation) north-west of its primary – the exoplanet host star HD 3651 at 11 pc. The companion, HD 3651 B, clearly shares the proper motion of the exoplanet host star in our four images, obtained with the European Southern Observatory New Technology Telescope and the United Kingdom Infrared Telescope, spanning three years in epoch difference. The magnitude of the companion is H= 16.75 ± 0.16 mag, the faintest co-moving companion of an exoplanet host star imaged directly. HD 3651 B is not detected in the POSS-II B-, R- or I-band images, indicating that this object is fainter than ∼20 mag in the B- and R-band and fainter than ∼19 mag in the I-band. With the Hipparcos distance of HD 3651 of 11 pc, the absolute magnitude of HD 3651 B is about 16.5 mag in the H band. Our H-band photometry and the Baraffe et al. (2003) evolutionary models yield a mass of HD 3651 B to be 20 to 60 MJup (Jupiter masses) for assumed ages between 1 and 10 Gyr. The effective temperature ranges between 800 and 900 K, consistent with a spectral type of T7 to T8. We conclude that HD 3651 B is a brown dwarf companion, the first of its kind directly imaged as a companion of an exoplanet host star, and one of the faintest T dwarfs found in the solar vicinity (within 11 pc).

Metallicity and absolute magnitude calibrations for UBV photometry

Metallicity and absolute magnitude calibrations for UBV photometry

Properties and nature of Be stars

' Department of Physics and Astronomy, Michigan State University, E. Lansing, MI, 48824 and Affiliate Professor, Department of Astronomy, University of Washington, Seattle, WA 98195, USA e-mail: linnell@astro.washington.edu 2 Astronomical Institute of the Charles University, Faculty of Mathematics and Physics, V Holesovickach 2, 180 00 Praha 8, Czech Republic 3 Astronomical Institute, Academy of Sciences, 251 65 Ondrejov, Czech Republic e-mail: hec@sunstel. asu. cas. cz 4 Hvar Observatory, Faculty of Geodesy, Kaciceva 26, 10000 Zagreb, Croatia e-mail: hbozic (dsudar, rdomagoj)@hvar.geof. hr 5 Department of Physics and Astronomy, University of Victoria, PO Box 3055 STN CSC, Victoria, B.C., V8W 3P6, Canada e-mail: yang@uvastro.plays..uvic.ca 6 Dept. of Astronomy, University of Guanajuato, 36000 Guanajuato, GTO, Mexico Aims. We include existing photometric and spectroscopic material with new observations in a detailed study of the Be+F binary V360 Lac. Methods. We used the programs FOTEL and KOREL to derive an improved linear ephemeris and to disentangle the line profiles of both binary components and telluric lines. The BINSYN software suite (described in the paper) is used to calculate synthetic light curves and spectra to fit the UBV photometry, an IUE spectrum, blue and red ground-based spectra, and observed radial-velocity curves. Results. The observations provide evidence of circumstellar matter in the system. The system model shows that the Be primary star is critically rotating, and that the synchronously rotating secondary star fills its Roche lobe. The primary star has a mass of 7.45 M ⊙ . Radial-velocity observations establish a mass ratio of 0.163. Light curve synthesis demonstrates that the observed light curves are controlled largely by tidal distortion and irradiation of the massive primary by the less massive secondary. Synthetic spectra fit both blue and red observed spectra with the exception of spectral lines affected by circumstellar matter in the system. The synthetic spectra allow for gravity darkening and are consistent with critical rotation of the primary. Synthetic spectrum fits to a dereddened IUE spectrum produce a calculated system distance of 512 pc. This distance is 2σ beyond the Hipparcos distance.

Resolving the Dusty Circumstellar Structure of the Enigmatic Symbiotic Star CH Cygni with the MMT Adaptive Optics System

We imaged the symbiotic star CH Cyg and two PSF calibration stars using the unique 6.5 m MMT deformable secondary adaptive optics system. Our high-resolution (FWHM = 03), very high Strehl (98% ± 2%), mid-infrared (9.8 and 11.7 μm) images of CH Cyg allow us to probe finer length scales than ever before for this object. CH Cyg is significantly extended compared to our unresolved PSF calibration stars (μ UMa and α Her) at 9.8 and 11.7 μm. We estimated the size of the extension by convolving a number of simple Gaussian models with the μ UMa PSF and determining which model provided the best fit to the data. Adopting the Hipparcos distance for this object of 270 pc, we found a nearly Gaussian extension with a FWHM at 9.8 μm of ~40.5 ± 2.7 AU (015 ± 001) and a FWHM at 11.7 μm of 45.9 ± 2.7 AU (017 ± 001). After subtracting out the Gaussian component of the emission (convolved with our PSF), we found a faint ~ 07 asymmetric extension, which peaks in flux ~05 north of the stars. This extension is roughly coincident with the northern knotlike feature seen in HST WFPC2 images obtained in 1999.

First Results from the CHARA Array. III. Oblateness, Rotational Velocity, and Gravity Darkening of Alderamin

We present observations of the A7 IV-V star Alderamin (α Cep, HR 8162, HD 203280) from the Georgia State University CHARA Array. These infrared interferometric angular size measurements indicate a noncircular projected disk brightness distribution for this known rapid rotator. The interferometric observations are modeled as arising from an elongated rigid atmosphere, with apparent polar and equatorial radii of rp = 0.6753 and re = 0.8767 mas, respectively, for a difference of 201 ± 32 μas, and with an axial ratio of re/rp = 1.298 ± 0.051. Using the Hipparcos distance of 14.96 ± 0.11 pc, these angular measures translate to 2.18 ± 0.05 and 2.82 ± 0.10 R☉. The inclination of Alderamin to the line of sight indicated by this modeling is effectively edge-on (i = 88.2 deg). The star has a true rotational velocity of 283 ± 10 km s-1 (~83% of breakup velocity) and a polar temperature of roughly 8400 K. Significantly, a necessary aspect of this modeling is a determination of the gravity-darkening coefficient, which at a value of β = 0.084 is consistent with a convective photosphere, as expected for an A7 IV-V star. Our detailed characterization of this object allows us to investigate various scenarios for the angular momentum history of Alderamin and the appropriateness of certain stellar evolution models.