arXiv subjects

L. H. Wasserman

Publications and source records attributed to L. H. Wasserman.

31 records · Page 2Linked to original sources

arXiv2004

The Solar Neighborhood IX: Hubble Space Telescope Detections of Companions to Five M and L Dwarfs within 10 pc of the Sun

We report the detections of low-mass companions to five M and L dwarfs within 10 pc of the Sun using the Hubble Space Telescope (HST) Near-Infrared Camera and Multi-Object Spectrometer (NICMOS). Follow-up observations using the HST Advanced Camera for Surveys (ACS) and Fine Guidance Sensor 1r (FGS1r) confirm our NICMOS discoveries of companions to the L4.5 dwarf GJ 1001B (LHS 102B) and the M5 dwarf LHS 224, respectively. Images obtained with the Astrophysical Research Consortium 3.5 m telescope at Apache Point Observatory verify our discovery of a companion to the M3 dwarf G 239-25. Our NICMOS images confirm the previously suspected duplicity of the M3 dwarfs GJ 54 and GJ 84. The components of GJ 1001BC and LHS 224AB have nearly equal luminosities in all the ACS and/or NICMOS bandpasses in which they were observed. The magnitudes of GJ 54A and B in one FGS1r bandpass and four NICMOS bandpasses differ by <~ 1. GJ 84B and G 239-25B are ~4 magnitudes fainter than their M3 companions in the NICMOS bandpasses. We estimate from our NICMOS photometry that GJ 84B and G 239-25B have spectral types M7 and M8, respectively, and masses near the lower limit for sustained hydrogen burning. The apparent separations of GJ 1001BC, GJ 54AB, and LHS 224AB suggest orbital periods less than 5 yr. These binary dwarfs are ideal candidates for continued astrometric monitoring that will quickly yield accurate dynamic masses needed to constrain the mass-luminosity relation for low-mass stars and brown dwarfs.

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arXiv2003

Resonant and Secular Families in the Kuiper Belt

We review ongoing efforts to identify occupants of mean-motion resonances (MMRs) and collisional families in the Edgeworth-Kuiper belt. Direct integrations of trajectories of Kuiper belt objects (KBOs) reveal the 1:1 (Trojan), 5:4, 4:3, 3:2 (Plutino), 5:3, 7:4, 9:5, 2:1 (Twotino), and 5:2 MMRs to be inhabited. Apart from the Trojan, resonant KBOs typically have large orbital eccentricities and inclinations. The observed pattern of resonance occupation is consistent with resonant capture and adiabatic excitation by a migratory Neptune; however, the dynamically cold initial conditions prior to resonance sweeping that are typically assumed by migration simulations are probably inadequate. Given the dynamically hot residents of the 5:2 MMR and the substantial inclinations observed in all exterior MMRs, a fraction of the primordial belt was likely dynamically pre-heated prior to resonance sweeping. A pre-heated population may have arisen as Neptune gravitationally scattered objects into trans-Neptunian space. The spatial distribution of Twotinos offers a unique diagnostic of Neptune's migration history. The Neptunian Trojan population may rival the Jovian Trojan population, and the former's existence is argued to rule out violent orbital histories for Neptune. Finally, lowest-order secular theory is applied to several hundred non-resonant KBOs with well-measured orbits to update proposals of collisional families. No convincing family is detected.

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arXiv2003

Procedures, Resources, and Selected Results of the Deep Ecliptic Survey

The Deep Ecliptic Survey is a project whose goal is to survey a large area of the near-ecliptic region to a faint limiting magnitude (R ~ 24) in search of objects in the outer solar system. We are collecting a large homogeneous data sample from the Kitt Peak Mayall 4-m and Cerro Tololo Blanco 4-m telescopes with the Mosaic prime-focus CCD cameras. Our goal is to collect a sample of 500 objects with good orbits to further our understanding of the dynamical structure of the outer solar system. This survey has been in progress since 1998 and is responsible for 272 designated discoveries as of March 2003. We summarize our techniques, highlight recent results, and describe publically available resources.

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arXiv2003

Astrometry with Hubble Space Telescope: A Parallax of the Central Star of the Planetary Nebula NGC 6853

We present an absolute parallax and relative proper motion for the central star of the planetary nebula NGC 6853 (The Dumbell). We obtain these with astrometric data from FGS 3, a white-light interferometer on {\it HST}. Spectral classifications and VRIJHKT$_2$M and DDO51 photometry of the stars comprising the astrometric reference frame provide spectrophotometric estimates of their absolute parallaxes. Introducing these into our model as observations with error, we find $π_{abs} = 2.10 \pm 0.48$ mas for the DAO central star of NGC 6853. A weighted average with a previous ground-based USNO determination yields $π_{abs} = 2.40 \pm 0.32$. We assume that the extinction suffered by the reference stars nearest (in angular separation and distance) to the central star is the same as for the central star. Correcting for color differences, we find $<$A$_V>$ = 0.30 $ \pm $ 0.06 for the central star, hence, an absolute magnitude M$_V = 5.48^{-0.16}_{+0.15}$. A recent determination of the central star effective temperature aided in estimating the central star radius, $R_{*}=0.055 \pm 0.02R_{\sun}$, a star that may be descending to the white dwarf cooling track.

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arXiv2003

Resonance Occupation in the Kuiper Belt: Case Examples of the 5:2 and Trojan Resonances

As part of our ongoing Deep Ecliptic Survey (DES) of the Kuiper belt, we report on the occupation of the 1:1 (Trojan), 4:3, 3:2, 7:4, 2:1, and 5:2 Neptunian mean-motion resonances (MMRs). The occupation of the 1:1 and 5:2 MMRs is not easily understood within the standard model of resonance sweeping by a migratory Neptune over an initially dynamically cold belt. Our dynamically hot, 5:2 resonant objects can librate with modest amplitudes of 90 deg within the resonance for at least 1 Gyr. Their trajectories cannot be explained by close encounters with Neptune alone, given the latter's current orbit. The hot orbits of such 5:2 resonant KBOs, unlike hot orbits of previously known resonant KBOs, may imply that these objects were pre-heated to large inclination and large eccentricity prior to resonance capture by a migratory Neptune. Our first discovered Neptunian Trojan, 2001QR322, may not owe its existence to Neptune's migration at all. The trajectory of 2001QR322 is remarkably stable; the object can undergo tadpole-type libration about Neptune's leading Lagrange (L4) point for at least 1 Gyr with a libration amplitude of 24 deg. Trojan capture probably occurred while Neptune accreted the bulk of its mass. For an assumed albedo of 12--4%, our Trojan is 130--230 km in diameter. Model-dependent estimates place the total number of Neptune Trojans resembling 2001QR322 at 20--60. Their existence might rule out violent orbital histories for Neptune.

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arXiv2002

Astrometry with Hubble Space Telescope: A Parallax of the Fundamental Distance Calibrator delta Cephei

We present an absolute parallax and relative proper motion for the fundamental distance scale calibrator, delta Cep. We obtain these with astrometric data from FGS 3, a white-light interferometer on HST. Utilizing spectrophotometric estimates of the absolute parallaxes of our astrometric reference stars and constraining delta Cep and reference star HD 213307 to belong to the same association (Cep OB6, de Zeeuw et al. 1999), we find pi_{abs} = 3.66 +/- 0.15 mas. The larger than typical astrometric residuals for the nearby astrometric reference star HD 213307 are found to satisfy Keplerian motion with P = 1.07 +/- 0.02 years, a perturbation and period that could be due to a F0V companion ~7 mas distant from and ~4 magnitudes fainter than the primary. Spectral classifications and VRIJHKT$_2$M and DDO51 photometry of the astrometric reference frame surrounding delta Cep indicate that field extinction is high and variable along this line of sight. However the extinction suffered by the reference star nearest (in angular separation and distance) to delta Cep, HD 213307, is lower and nearly the same as for delta Cep. Correcting for color differences, we find = 0.23 +/- 0.03 for delta Cep, hence, an absolute magnitude M_V = -3.47 +/- 0.10. Adopting an average V magnitude, = 15.03 +/- 0.03, for Cepheids with log P = 0.73 in the LMC from Udalski et al. (1999), we find a V-band distance modulus for the LMC, m-M = 18.50 +/- 0.13 or, 18.58 +/- 0.15, where the latter value results from a highly uncertain metallicity correction (Freedman et al. 2001). These agree with our previous RR Lyr HST parallax-based determination of the distance modulus of the LMC.

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arXiv2001

Astrometry with Hubble Space Telescope: A Parallax of the Fundamental Distance Calibrator RR Lyrae

We present an absolute parallax and relative proper motion for the fundamental distance scale calibrator, RR Lyr. We obtain these with astrometric data from FGS 3, a white-light interferometer on HST. We find $π_{abs} = 3.82 \pm 0.2$ mas. Spectral classifications and VRIJHKT$_2$M and DDO51 photometry of the astrometric reference frame surrounding RR Lyr indicate that field extinction is low along this line of sight. We estimate =0.07\pm0.03 for these reference stars. The extinction suffered by RR Lyr becomes one of the dominant contributors to the uncertainty in its absolute magnitude. Adopting the average field absorption, =0.07 \pm 0.03, we obtain M_V^{RR} = 0.61 ^{-0.11}_{+0.10}. This provides a distance modulus for the LMC, m-M = 18.38 - 18.53^{-0.11}_{+0.10} with the average extinction-corrected magnitude of RR Lyr variables in the LMC, , remaining a significant uncertainty. We compare this result to more than 80 other determinations of the distance modulus of the LMC.

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arXiv2001

Interferometric Astrometry with Hubble Space Telescope Fine Guidance Sensor 3:The Parallax of the Cataclysmic Variable TV Columbae

TV Columbae (TV Col) is a 13th magnitude Intermediate Polar (IP) Cataclysmic Variable (CV), with multiple periods found in the light curves. Past estimates predicted a distance of 400 parsec to greater than 500 parsec. Recently completed Hubble Space Telescope (HST) Fine Guidance Sensor (FGS) interferometric observations allow us to determine the first trigonometric parallax to TV Col. This determination puts the distance of TV Col at 368 -15+17 parsecs. CD-32 2376, a 10th magnitude Tycho Catalog star, is a reference star in the TV Col frame. We find a distance of $127.7 -1+1 parsecs.

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arXiv2000

Precise Masses for Wolf 1062 AB from Hubble Space Telescope Interferometric Astrometry and McDonald Observatory Radial Velocities

We present an analysis of astrometric data from FGS 3, a white-light interferometer on {\it HST}, and of radial velocity data from two ground-based campaigns. We model the astrometric and radial velocity measurements simultaneously to obtain parallax, proper motion and component masses for Wolf 1062 = Gl 748 AB (M3.5V). To derive the mass fraction, we relate FGS 3 fringe scanning observations of the science target to a reference frame provided by fringe tracking observations of a surrounding star field. We obtain an absolute parallax $π_{abs} = 98.0 \pm 0.4$ milliseconds of arc, yielding ${\cal M}_A = 0.379 \pm 0.005{\cal M}_{\sun}$ and ${\cal M}_B= 0.192 \pm 0.003 {\cal M}_{\sun}$, high quality component masses with errors of only 1.5%.

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arXiv2000

Interferometric Astrometry of the Detached White Dwarf - M Dwarf Binary Feige 24 Using Hubble Space Telescope Fine Guidance Sensor 3: White Dwarf Radius and Component Mass Estimates

With HST FGS 3 we have determined a parallax for the white dwarf - M dwarf interacting binary, Feige 24. The white dwarf (DA) component has an effective temperature, T_eff of approximately 56,000 K degrees. A weighted average with past parallax determinations (pi_abs = 14.6 +- 0.4 milliseconds of arc) narrows the range of possible radius values, compared to past estimates. We obtain R_DA = 0.0185 +- 0.0008 R_solar with uncertainty in the temperature and bolometric correction the dominant contributors to the error. FGS photometry provides a light curve entirely consistent with reflection effects. A recently refined model Mass-Luminosity Relation (Baraffe et al. 1998) for low mass stars provides a mass estimate for the M dwarf companion, M_dM = 0.37 +- 0.20 M_solar, where the mass range is due to metallicity and age uncertainties. Radial velocities from Vennes and Thorstensen (1994) provide a mass ratio from which we obtain M_DA = 0.49+0.19-0.05 ~ M_solar. Independently, our radius and recent log_g determinations yield 0.44 < M_DA < 0.47 M_solar. In each case the minimum DA mass is that derived by Vennes & Thorstensen from their radial velocities and Keplerian circular orbits with inclination <= 90 degrees. Locating Feige 24 on an M - R plane suggests a carbon core. Our radius and these mass estimates yield a gamma_grav inconsistent with that derived by Vennes & Thorstensen. We speculate on the nature of a third component whose existence would resolve the discrepancy.

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arXiv1999

Interferometric Astrometry of Proxima Centauri and Barnard's Star Using Hubble Space Telescope Fine Guidance Sensor 3: Detection Limits for sub-Stellar Companions

We report on a sub-stellar companion search utilizing interferometric fringe-tracking astrometry acquired with Fine Guidance Sensor 3 (FGS 3) on the Hubble Space Telescope. Our targets were Proxima Centauri and Barnard's Star. We obtain absolute parallax values for Proxima Cen pi_{abs} = 0.7687 arcsecond and for Barnard's Star pi_{abs} = 0.5454 arcsecond. Once low-amplitude instrumental systematic errors are identified and removed, our companion detection sensitivity is less than or equal to one Jupiter mass for periods longer than 60 days for Proxima Cen. Between the astrometry and the radial velocity results we exclude all companions with M > 0.8M_{Jup} for the range of periods 1 < P < 1000 days. For Barnard's Star our companion detection sensitivity is less than or equal to one Jupiter mass for periods long er than 150 days. Our null results for Barnard's Star are consistent with those of Gatewood (1995).

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arXiv1999

Astrometry with Hubble Space Telescope Fine Guidance Sensor 3: The Parallax of the Cataclysmic Variable RW Triangulum

RW Triangulum (RW Tri) is a 13th magnitude Nova-like Cataclysmic Variable star with an orbital period of 0.2319 days (5.56 hours). Infrared observations of RW Tri indicate that its secondary is most likely a late K-dwarf. Past analyses predicted a distance of 270 parsec, derived from a black-body fit to spectrum of the central part of the disk. Recently completed Hubble Space Telescope Fine Guidance Sensor interferometric observations allow us to determine the first trigonometric parallax to RW Tri. This determination puts the distance of RW Tri at 341, one of the most distant objects with a direct parallax measurement.

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arXiv1998

Photometry of Proxima Centauri and Barnard's Star Using HST Fine Guidance Sensor 3: A Search for Periodic Variations

We have observed Proxima Centauri and Barnard's Star with Hubble Space Telescope Fine Guidance Sensor 3. Proxima Centauri exhibits small-amplitude, periodic photometric variations. Once several sources of systematic photometric error are corrected, we obtain 2 milli-magnitude internal photometric precision. We identify two distinct behavior modes over the past four years: higher amplitude, longer period; smaller amplitude, shorter period. Within the errors one period (P ~ 83d) is twice the other. Barnard's Star shows very weak evidence for periodicity on a timescale of approximately 130 days. If we interpret these periodic phenomena as rotational modulation of star spots, we identify three discrete spots on Proxima Cen and possibly one spot on Barnard's Star. We find that the disturbances change significantly on time scales as short as one rotation period.

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