Parallax Observations Research Articles

The Distance to the Vela Pulsar Gauged withHubble Space TelescopeParallax Observations

The distance to the Vela pulsar (PSR B0833-45) has been traditionally assumed to be 500 pc. Although affected by a significant uncertainty, this value stuck to both the pulsar and the supernova remnant. In an effort to obtain a model-free distance measurement, we have applied high-resolution astrometry to the pulsar V ~ 23.6 optical counterpart. Using a set of five Hubble Space Telescope Wide Field Planetary Camera 2 observations, we have obtained the first optical measurement of the annual parallax of the Vela pulsar. The parallax turns out to be 3.4 ± 0.7 mas, implying a distance of 294 pc, i.e., a value significantly lower than previously believed. This affects the estimate of the pulsar absolute luminosity and of its emission efficiency at various wavelengths and confirms the exceptionally high value of Ne toward the Vela pulsar. Finally, the complete parallax database allows for a better measurement of the Vela pulsar proper motion [μα cos(δ) = -37.2 ± 1.2 mas yr-1; μδ = 28.2 ± 1.3 mas yr-1 after correcting for the peculiar motion of the Sun], which, at the parallax distance, implies a transverse velocity of ≈65 km s-1. Moreover, the proper-motion position angle appears especially well aligned with the axis of symmetry of the X-ray nebula as seen by Chandra. Such an alignment allows us to assess the space velocity of the Vela pulsar to be 81 km s-1.

The Distance to the Hyades Cluster Based on [ITAL]Hubble Space Telescope[/ITAL] Fine Guidance Sensor Parallaxes

Trigonometric parallax observations made with the Hubble Space Telescope (HST) Fine Guidance Sensor (FGS) 3 of seven Hyades members in six fields of view have been analyzed along with their proper motions to determine the distance to the cluster. Knowledge of the convergent point and mean proper motion of the Hyades is critical to the derivation of the distance to the center of the cluster. Depending on the choice of the proper-motion system, the derived cluster center distance varies by 9%. Adopting a reference distance of 46.1 pc or m - M = 3.32, which is derived from the ground-based parallaxes in the General Catalogue of Trigonometric Stellar Parallaxes (1995 edition), the FK5/PPM proper-motion system yields a distance 4% larger, while the Hanson system yields a distance 2% smaller. The HST FGS parallaxes reported here yield either a 14% or 5% larger distance, depending on the choice of the proper-motion system. Orbital parallaxes (Torres et al.) yield an average distance 4% larger than the reference distance. The variation in the distance derived from the HST data illustrates the importance of the proper-motion system and the individual proper motions to the derivation of the distance to the Hyades center; therefore, a full utilization of the HST FGS parallaxes awaits the establishment of an accurate and consistent proper-motion system.

Photon Statistics Limits for Earth‐based Parallax Measurements of Events

We analyze the limitations imposed by photon counting statistics on extracting useful information about MACHOs from Earth-based parallax observations of microlensing events. We find that if one or more large (say $2.5\,\rm m$) telescopes are dedicated to observing a MACHO event for several nights near maximum amplification, then it is possible, in principle, to measure the velocity of the MACHO well enough to distinguish between disk and halo populations for events with $\omega {A_m}\!^2 \gta 1\,\rm day^{-1}$, where $\omega^{-1}$ denotes the timescale of the event and $A_m$ denotes its maximum amplification. Thus, if it turns out to be possible to reduce all other sources of error to below that of photon statistics, it may be feasible to do useful Earth-based parallax observations for high amplification events.

Parallax Observations with the [ITAL]Hubble Space Telescope[/ITAL] Yield the Distance to Geminga

Using data from Hubble Space Telescope observations, we report the first optical measurement of the annual parallax of a neutron star. This is the counterpart of the X-ray/γ-ray pulsar Geminga, for which strong proper motion has already been reported. Significant displacement from such motion is detected using WFPC2 observations, taken at the dates of the maximum predicted parallactic factor. The resulting distance value is 157 pc (+59, -34), just consistent with the lower end of the wide range derived from X-ray data.

Analysis of a [ITAL]Hubble Space Telescope[/ITAL] Search for Red Dwarfs: Limits on Baryonic Matter in the Galactic Halo

We reexamine a deep Hubble Space Telescope pencil-beam search for red dwarfs, stars just massive enough to burn hydrogen. The authors of this search (Bahcall et al.) found that red dwarfs make up less than 6% of the Galactic halo. First, we extrapolate this result to include brown dwarfs, stars not quite massive enough to burn hydrogen; we assume a 1/ mass function. Then the total mass of red dwarfs and brown dwarfs is ≤18% of the halo. This result is consistent with microlensing results, assuming a popular halo model. However, using new stellar models and parallax observations of low-mass, low-metallicity stars, we obtain much tighter bounds on low-mass stars. We find the halo red dwarf density to be less than 1% of the halo, while our best estimate of this value is 0.14%-0.37%. Thus, our estimate of the halo mass density of red dwarfs drops to 16-40 times less than the result reported by Bahcall et al. in 1994. For a 1/ mass function, this suggests a total density of red dwarfs and brown dwarfs of ~0.25%-0.67% of the halo, i.e., (0.9-2.5) × 109 ☉ out to 50 kpc. Such a low result would conflict with microlensing estimates by the MACHO group. We suggest that either the halo mass function must rise very steeply below the hydrogen-burning limit or the microlensing results should be reinterpreted with a different halo model or mass function.

Transverse velocities of galaxies from microlens parallexes

The transverse velocity of a spiral galaxy can be measured to an accuracy $\sim 60\,\kms$ by making parallax observations of quasars being microlensed by stars in the disk of the galaxy. To make the measurement, a quasar must be located behind the disk of the galaxy between about 1 and 2 scale lengths from the center. The quasar must then be monitored for microlensing events and the events followed simultaneously from the Earth and a satellite in solar orbit, preferably at $\sim 30\,$AU. A systematic search in a volume within $21,000\,\kms$ could locate quasars with $B<23$ behind a total of $\sim 1900$ galaxies. The rate of lensing events (and hence galaxy velocity measurements) would be $\sim 3\,{\rm yr}^{-1}$. The events would have typical characteristic times $\omega^{-1}\sim 3\,$yr. Under the assumption that the mass spectrum of lensing objects is the same in other spiral galaxies as in our own, the observations could be used to measure the Hubble parameter to an accuracy of 5\%.

The measurement of astronomical parallaxes with CCD imaging cameras on small telescopes

Small telescopes equipped with charge-coupled device (CCD) imaging cameras are well suited to introductory laboratory exercises in positional astronomy (astrometry). An elegant example is the determination of the parallax of extraterrestrial objects, such as asteroids. For laboratory exercises suitable for introductory students, the astronomical hardware needs are relatively modest, and, under the best circumstances, the analysis requires little more than arithmetic and a microcomputer with image display capabilities. Results from the first such coordinated parallax observations of asteroids ever made are presented. In addition, procedures for several related experiments, involving single-site observations and/or parallaxes of earth-orbiting artificial satellites, are outlined.

Summary remarks to discussion on parallaxes

A number of general conclusions can be drawn from this morning’s discussions. Unfortunately most of them have been well known for many years. That fact alone should cause us to seriously consider Dr. Lutz’s suggestion that standard parallax regions be adopted for the continuous calibration of accidental and systematic errors of parallax observations now being made. In this way we will be able to put our modern observations on a standard system with some degree of confidence. On the other hand the problem is now to make the best possible use of the previously published data for which no such reliable calibration exists.

Internal and external errors in trigonometric parallaxes

The methods for evaluating internal and external errors in parallaxes are reviewed and the results of each method are examined. The influence on parallax errors of variations in the weighting of individual parallax observations and of variations in reference-star configurations is discussed with emphasis placed on recent investigations of these effects made at the Van Vleck Observatory.

Proper Motion and Parallax Programmes for Large Telescopes

Proper motion work at the present time relies on the availability of plates taken in the past, for which the magnitude limit is generally not fainter than about mpg = 16, apart from Luyten's survey with the Palomar Schmidt. It is very important for future studies to fainter magnitudes in, for example, star clusters, that sufficient time is made available on large telescopes so that plates can be taken now. Consideration should also be given to an extension of proper motion work in Selected Areas.Ideally, trigonometric parallax observations are best carried out on a dedicated telescope, such as the USNO 61-in. reflector, with a large amount of time available; but if sufficient observational material is to be obtained on faint stars, time must also be taken on other medium sized and large reflectors. With the severe limitation of time available on these telescopes, the criteria for selection of stars for such programmes become of prime importance. Large Schmidt telescopes, with fast automatic plate measurement, may possibly be used for surveys of nearby stars, unbiased by any kinematic or photometric selection effects.

The parallax of Luyten 726-8.

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The parallax of Luyten 726-8. Wagman, N. E. Abstract The low altitude and faintness of this star make parallax observations difficult at Allegheny. However, 147 images taken on 48 nights since August 1949 have been measured. The images are usually elongated, fuzzy, and weak but sometimes the two components of the star are almost separated. In any case the estimated center of gravity of the images is measured. Poor distribution of the plates between morning and evening also detracts from this determination. Solutions for the parallax in a and ~ were made for all 48 plates. Then the plates best suited for a parallax determination were selected and new solutions made. The results were: a (48 plates) +0'.'323+0'.'022 a (27 plates) + .324+ .oi8 ~ (48 plates) + .371+ .041 ~ (26 plates) + .383+ .043 Ir (48 plates) + .333+ .019 Ir (27and26) + .333+ .016 The last two lines result from combining the solutions in a and ~. The value + "333 is considerably lower than the value + `.`41 obtained from short series of observations at other places. However, the likelihood remains that each of the components of Luyten 726-8 is less massive than Ross 614 B, or o.o8 of the mass of the sun. A llegheny Observatory, University of Pittsburgh, Pittsburgh, Pa. Publication: The Astronomical Journal Pub Date: 1956 DOI: 10.1086/107396 Bibcode: 1956AJ.....61Q.191W full text sources ADS |

SPECTROSCOPIC BINARIES AND THEIR PARALLAXES

It is well known that the presence of invisible or faint companions of some stars has been predicted before these companions were actually discovered by telescopic means. The classic examples are Sirius and Procyon, for which Bessel in 1844 predicted, from irregularities in their proper motions, the existence of faint companions, which were discovered in 1861 and 1896, respectively, with powerful telescopes. C Cancri is a triple system consisting of two bodies A and B that revolve around each other in about 60 years, and a third body C that revolves around AB in about 677 years, but in an irregular way, which according to Seeliger can be explained by the presence of a dark body, revolving around C in 18 years. Later investigations give 17 years for this period, and it seems established that this fourth body is present, though it has never been found visually or spectroscopically. In I; Ursae Majoris the two components revolve around each other in 59.9 years, but Norlund found a perturbation with a period of 1.8 years in their motion and suggested the presence of an invisible companion. Earlier, Wright had announced that the bright component is a spectroscopic binary, and an examination of his plates indicated a period very close to the period of 1 . 8 years found by Norlund and later confirmed by Hertzsprung from photographic observations of the system. C Aquarii has recently been investigated by Strand.1 Its period is 400 years, but the deviations of the observations from Keplerian motion are large and regular, indicating the presence of a third, invisible body which revolves around one of the visible components in a circular orbit with a period of 25 years. Modern trigonometric parallax observations constitute the most accurate determinations of relative positions of stars. They are so accurate that it should well be possible, as pointed out by

The Correction of a Group of Parallax Observations and the Determination of the Main Series

The Correction of a Group of Parallax Observations and the Determination of the Main Series

A Method for Correcting Series of Parallax Observations

A Method for Correcting Series of Parallax Observations

On the proposed Parallax Observations of Mars in 1862

On the proposed Parallax Observations of Mars in 1862