Browsing by Subject "interferometric astrometry"
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Item Astrometry With The Hubble Space Telescope: Trigonometric Parallaxes Of Planetary Nebula Nuclei NGC 6853, NGC 7293, Abell 31, And Deht 5(2009-12) Benedict, G. Fritz; McArthur, Barbara E.; Napiwotzki, Ralph; Harrison, Thomas E.; Harris, Hugh C.; Nelan, Edmund; Bond, Howard E.; Patterson, Richard J.; Ciardullo, Robin; Benedict, G. Fritz; McArthur, Barbara E.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. Proper motions, spectral classifications and VJHKT(2)M 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, sigma(pi)/pi = 5%. Derived distances are: d(NGC6853) = 405(-25)(+28) pc, d(NGC7293) = 216(-12)(+14) pc, d(Abell 31) = 621(-70)(+91) pc, and d(DeHt 5) = 345(-17)(+19) pc. These PNNi distances are all smaller than previously derived from spectroscopic analyses of the central stars. To obtain absolute magnitudes from these distances requires estimates of interstellar extinction. We average extinction measurements culled from the literature, from reddening based on PNNi intrinsic colors derived from model SEDs, and an assumption that each PNN experiences the same rate of extinction as a function of distance as do the reference stars nearest (in angular separation) to each central star. We also apply Lutz-Kelker bias corrections. The absolute magnitudes and 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-circle dot, 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.Item The Mass Of The Candidate Exoplanet Companion To HD 136118 From Hubble Space Telescope Astrometry And High-Precision Radial Velocities(2010-01) Martioli, Elder; McArthur, Barbara E.; Benedict, G. Fritz; Bean, Jacob L.; Harrison, Thomas E.; Armstrong, Amber; McArthur, Barbara E.; Benedict, G. Fritz; Armstrong, AmberWe use Hubble Space Telescope fine guidance sensor astrometry and high-cadence radial velocities for HD 136118 from the Hobby-Eberly Telescope with archival data from Lick to determine the complete set of orbital parameters for HD 136118 b. We find an orbital inclination for the candidate exoplanet of i(b) = 163 degrees.1 +/- 3 degrees.0. This establishes the actual mass of the object, M(b) = 42(-18)(+11) M(J), in contrast to the minimum mass determined from the radial velocity data only, M(b) sin i similar to 12 M(J). Therefore, the low-mass companion to HD 136118 is now identified as a likely brown dwarf residing in the "brown dwarf desert."Item Modeling Multi-Wavelength Stellar Astrometry. I. Sim Lite Observations Of Interacting Binaries(2010-07) Coughlin, Jeffrey L.; Gelino, Dawn M.; Harrison, Thomas E.; Hoard, D. W.; Ciardi, David R.; Benedict, G. Fritz; Howell, Steve B.; McArthur, Barbara E.; Wachter, Stefanie; Benedict, G. Fritz; McArthur, Barbara E.Interacting binaries (IBs) consist of a secondary star that 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 to allow us to model the flux-weighted reflex motions of IBs, in a code we call reflux. This code gives us sufficient flexibility to investigate nearly every configuration of IB. We find that SIM Lite will be able to determine astrometric orbits for all sufficiently bright IBs 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.