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At the IAU XXVI General Assembly in 2006, the Division I decided to create the Working Group on Astrometry by Small Ground-Based Telescopes (WG-ASGBT). Its scientic goals are to foster the follow-up of small bodies detected by the large surveys including the NEOs; to set-up a dedicated observation network for the follow-up of objects which will be detected by Gaia; to contribute to the observation campaigns of the mutual events of natural satellites, stellar occultations, and binary asteroids; and to encourage teaching astrometry for the next generation. The present report gives the main activities carried out in these areas with small telescopes (diameter less than 2m).

A proper motion study of a field of 20' x 20' inside Plaut's low extinction window (l,b)=(0 deg,-8 deg), has been completed. Relative proper motions and photographic BV photometry have been derived for ~21,000 stars reaching to V~20.5 mag, based on the astrometric reduction of 43 photographic plates, spanning over 21 years of epoch difference. Proper motion errors are typically 1 mas/yr and field dependent systematics are below 0.2 mas/yr. Cross-referencing with the 2MASS catalog yielded a sample of ~8,700 stars, from which predominantly disk and bulge subsamples were selected photometrically from the JH color-magnitude diagram. The two samples exhibited different proper-motion distributions, with the disk displaying the expected reflex solar motion as a function of magnitude. Galactic rotation was also detected for stars between ~2 and ~3 kpc from us. The bulge sample, represented by red giants, has an intrinsic proper motion dispersion of (sigma_l,sigma_b)=(3.39, 2.91)+/-(0.11,0.09) mas/yr, which is in good agreement with previous results, and indicates a velocity anisotropy consistent with either rotational broadening or tri-axiality. A mean distance of 6.37^{+0.87}_{-0.77} kpc has been estimated for the bulge sample, based on the observed K magnitude of the horizontal branch red clump. The metallicity [M/H] distribution was also obtained for a subsample of 60 bulge giants stars, based on calibrated photometric indices. The observed [M/H] shows a peak value at [M/H]~-0.1 with an extended metal poor tail and around 30% of the stars with supersolar metallicity. No change in proper motion dispersion was observed as a function of [M/H]. We are currently in the process of obtaining CCD UBVRI photometry for the entire proper-motion sample of ~21,000 stars., Comment: Submitted to AJ April 17th 2007. Accepted June 8th 2007. 45 pages, 14 figures

Using parallaxes and proper motions of a kinematically and spatially unbiased sample of old bright red giant stars from the Hipparcos catalog with measured radial velocities from Barbier-Brossat & Figon (2000), we have re-estimated the surface density of the Galactic disk in the solar neighbourhood within ±0.4 kpc of the Sun. We determine the vertical distribution of the red giants as well as the vertical velocity dispersion of the sample, (14.4±0.26 km/sec), and combine these to derive the surface density of gravitating matter in the Galactic disk. Using these data, we determine the surface density of the galactic disk as a function of the galactic coordinate, z. the surface density of the disk increases from 10.5 ±0.5 M⊙within ±50 pc to 42 ±6 M⊙/pc2 within ±350 pc. The volume density of the galactic disk within ±50 pc is 0.105±0.005 M⊙/pc3, which is only marginally greater (within 2 sigma) than the volume density estimates of observed baryonic matter in the solar neighbourhood.

A continuation of this WG was voted for at the IAU GA 2006 in Prague. The International Celestial Reference Frame (ICRF) is defined by the positions of 212 distant quasars at radio wavelengths. The primary, optical reference frame is the Hipparcos Celestial Reference Frame (HCRF), which is the Hipparcos Catalog without astrometric ‘problem’ stars (in: H. Rickman (ed.) 2001, Proceedings IAU XXIV General Assembly, Transactions IAU XXIVB (San Francisco: ASP), Resolution B1.2). The Tycho-2 catalog with its 2.5 million brightest stars forms the first step in the densification of the optical reference frame. However, the limiting magnitude of about V = 12 of the Tycho-2 catalog is not sufficient for most applications in astronomy and the goal of this IAU Working Group is to further extend the grid of highly accurate positions and motions toward more and fainter stars. The web site of this WG is at .

The calibration of luminosities using trigonometric parallaxes introduces well-known errors that are a function of the ratio of the parallax error to the parallax, when the sample is chosen from stars with measured parallaxes larger than some minimum parallax. In this paper it is shown that similar errors are also introduced into the mass axis of the mass-luminosity relation (MLR) and can result in a biased MLR. The bias is shown to be related to the Lutz-Kelker correction to the absolute magnitude, as extended by Hanson for the case of selection effects in the data sample. The size of the correction in the mass axis is substantial and for the case of a uniform distribution in space, it can amount to a multiplicative factor of 1.17 in the mass for a ten sigma (σ/π = 0.10) parallax and a factor of 1.62 for a five sigma (σ/π = 0.20) parallax.

A program of follow-up observations of HIPPARCOS Double Stars has been started using the WIYN 3.5-m Telescope at Kitt Peak, Arizona. Observations are made with the recently-completed RYTSI speckle camera, which is capable of determining reliable magnitude differences at various wavelengths down to the diffraction limit of the telescope. Thus in addition to precise relative astrometry, component magnitudes and colors can be obtained in a survey mode for all systems observed. Preliminary results and system capabilities are described. The benefits of a sustained program of observations of the HIPPARCOS Double Stars include populating the mass-luminosity relation with many more points (once the orbital status of these stars is known and orbital parameters are determined in sufficient detail for gravitationally bound pairs), robust tests of stellar evolution calculations in cases where at least one component has evolved off the main sequence, and a more complete picture of the nearby field binary population.

One of the continuing problems facing Commission 24 is its name. It has been known and reported for some years that the present title is not suitable for reasons that are all too obvious. This problem has continued during the last three years, despite the growing development and use of non-photographic methods and techniques.Most of the recent meeting activity in which the Commission and its membership has been involved, has centered on its shared interests with Commission 8 and with the Working Group on reference frames formed at the last General Assembly. Since its inception at that time, C. A. Murray has been appointed to represent the Commission on that group.

The objective of this investigation is the determination of absolute parallaxes and proper motions with respect to faint galaxies for three fields at mid galactic latitudes and one field near the south galactic pole. The three mid galactic latitude fields were photographed on a IIIa-J + GG385 plate/filter combination by van Altena at the prime focus of the KPNO 4-meter in the mid 1970s, while the south polar region was photographed on a IIIa-F + RG610 plate/filter combination by van Altena and C.E. Lopez (Univ. of San Juan, Argentina) at the prime focus of the CTIO 4-meter; all plates were hypersensitized by baking and exposed to the sky limit. In this paper we report on the progress of an investigation of the mid galactic latitude field at R.A. = 7h 07m 31s and Dec. = +7o 19.7′ (1950) which contains the faint binary white dwarf LP543-32/33. Preliminary measurements of selected stars in this field were made some time ago and a parallax of the white dwarf binary were published by van Altena and Mora (1977). Those measurements showed that the plates were of very high astrometric quality and that it would be possible to obtain accurate parallaxes for very faint stars.