arXiv subjects

Andrew F. Boden

Publications and source records attributed to Andrew F. Boden.

23 records · Page 2Linked to original sources

arXiv2007

Measurement of the Surface Gravity of $η$ Boo

Direct angular size measurements of the G0IV subgiant $η$ Boo from the Palomar Testbed Interferometer are presented, with limb-darkened angular size of $θ_{LD}= 2.1894^{+0.0055}_{-0.0140} $ mas, which indicate a linear radius of $R=2.672 \pm 0.028 R_\odot$. A bolometric flux estimate of $F_{BOL} = 22.1 \pm 0.28\times 10^{-7}$ erg cm$^{-2}$s$^{-1}$ is computed, which indicates an effective temperature of $T_{EFF}=6100 \pm 28$ K and luminosity of $L = 8.89 \pm 0.16 L_\odot$ for this object. Similar data are established for a check star, HD 121860. The $η$ Boo results are compared to, and confirm, similar parameters established by the {\it MOST} asteroseismology satellite. In conjunction with the mass estimate from the {\it MOST} investigation, a surface gravity of $\log g=3.817 \pm 0.016$ [cm s$^{-2}$] is established for $η$ Boo.

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arXiv2006

The Angular Diameter of $λ$ Boötis}

Using the CHARA Array and the Palomar Testbed Interferometer, the chemically peculiar star $λ$ Boötis has been spatially resolved. We have measured the limb darkened angular diameter to be $θ_{LD} = 0.533\pm0.029$ mas, corresponding to a linear radius of $R_{\star} = 1.70 \pm 0.10 R_\odot$. The measured angular diameter yields an effective temperature for $λ$ Boo of $T_{eff} = 8887 \pm 242$ K. Based upon literature surface gravity estimates spanning $\log{(g)} = 4.0-4.2$ $[\rm{cm s}^{-\rm{2}}]$, we have derived a stellar mass range of $M_{\star} = 1.1 - 1.7$ $M_\odot$. For a given surface gravity, the linear radius uncertainty contributes approximately $σ(M_\star) = 0.1-0.2 M_\odot$ to the total mass uncertainty. The uncertainty in the mass (i.e., the range of derived masses) is primarily a result of the uncertainty in the surface gravity. The upper bound of our derived mass range ($\log(g)=4.2, M_\star = 1.7\pm0.2 M_\odot$) is consistent with 100-300 MYr solar-metallicity evolutionary models. The mid-range of our derived masses ($\log(g)=4.1, M_\star = 1.3\pm0.2 M_\odot$) is consistent with 2-3 GYr metal-poor evolutionary models. A more definitive surface gravity determination is required to determine a more precise mass for $λ$ Boo.

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arXiv2006

A Physical Orbit for the High Proper Motion Binary HD 9939

We report spectroscopic and interferometric observations of the high-proper motion double-lined binary system HD 9939, with an orbital period of approximately 25 days. By combining our radial-velocity and visibility measurements we estimate the system physical orbit and derive dynamical masses for the components of $M_A = 1.072 \pm 0.014$ M$_{\sun}$ and $M_B = 0.8383 \pm 0.0081$ M$_{\sun}$; fractional errors of 1.3% and 1.0%, respectively. We also determine a system distance of $42.23 \pm 0.21$ pc, corresponding to an orbital parallax of $π_{\rm orb} = 23.68 \pm 0.12$ mas. The system distance and the estimated brightness difference between the stars in $V$, $H$, and $K$ yield component absolute magnitudes in these bands. By spectroscopic analysis and spectral energy distribution modeling we also estimate the component effective temperatures and luminosities as $T_{\rm eff}^A = 5050 \pm 100$ K and $T_{\rm eff}^B = 4950 \pm 200$ K and $L_A$ = 2.451 $\pm$ 0.041 $L_{\sun}$ and $L_B$ = 0.424 $\pm$ 0.023 $L_{\sun}$. Both our spectral analysis and comparison with stellar models suggest that HD 9939 has elemental abundances near solar values. Further, comparison with stellar models suggests the HD 9939 primary has evolved off the main sequence and appears to be traversing the Hertzsprung gap as it approaches the red giant phase of its evolution. Our measurements of the primary properties provide new empirical constraints on stellar models during this particularly dynamic evolutionary phase. That HD 9939 is currently in a relatively short-lived evolutionary state allows us to estimate the system age as 9.12 $\pm$ 0.25 Gyr. In turn the age and abundance of the system place a potentially interesting, if anecdotal, constraint on star formation in the galactic disk.

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arXiv2005

Testing Stellar Models With An Improved Physical Orbit for 12 Bootis

We report on a significantly improved determination of the physical orbit of the double-lined spectroscopic binary system 12 Boo. We have a 12 Boo interferometry dataset spanning six years with the Palomar Testbed Interferometer, a smaller amount of data from the Navy Prototype Optical Interferometer, and a radial velocity dataset spanning 14 years from the Harvard-Smithsonian Center for Astrophysics. We have updated the 12 Boo physical orbit model with our expanded interferometric and radial velocity datasets. The revised orbit is in good agreement with previous results, and the physical parameters implied by a combined fit to our visibility and radial velocity data result in precise component masses and luminosities. In particular, the orbital parallax of the system is determined to be 27.74 $\pm$ 0.15 mas, and masses of the two components are determined to be 1.4160 $\pm$ 0.0049 M$_{\sun}$ and 1.3740 $\pm$ 0.0045 M$_{\sun}$, respectively. Based on theoretical models we can estimate a system age of approximately 3.2 Gyr. Comparisons with stellar models suggest that the 12 Boo primary may be just entering the Hertzsprung gap, but that conclusion is highly dependent on details of the models. Such a dynamic evolutionary state makes the 12 Boo system a unique and important test for stellar models.

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arXiv2002

An interferometric-spectroscopic orbit for the binary HD 195987: Testing models of stellar evolution for metal-poor stars

We report spectroscopic and interferometric observations of the moderately metal-poor double-lined binary system HD 195987, with an orbital period of 57.3 days. By combining our radial-velocity and visibility measurements we determine the orbital elements and derive absolute masses for the components of M(A) = 0.844 +/- 0.018 Msun and M(B) = 0.6650 +/- 0.0079 Msun, with relative errors of 2% and 1%, respectively. We also determine the orbital parallax, pi(orb) = 46.08 +/- 0.27 mas, corresponding to a distance of 21.70 +/- 0.13 pc. The parallax and the measured brightness difference between the stars in V, H, and K yield the component absolute magnitudes in those bands. We also estimate the effective temperatures of the stars as Teff(A) = 5200 +/- 100 K and Teff(B) = 4200 +/- 200 K. Together with detailed chemical abundance analyses from the literature giving [Fe/H] approximately -0.5 (corrected for binarity) and [alpha/Fe] = +0.36, we use these physical properties to test current models of stellar evolution for metal-poor stars. Among the four that we considered, we find that no single model fits all observed properties at the measured composition, although we identify the assumptions in each one that account for the discrepancy and we conclude that a model with the proper combination of assumptions should be able to reproduce all the radiative properties. The indications from the isochrone fits and the pattern of enhancement of the metals in HD 195987 are consistent with this being a thick disk object, with an age of 10-12 Gyr.

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