LHS 17 - High Proper Motion Star


Overview

Since the proper motion of a star is inversely proportional to its distance, high proper motion is a filter for identifying nearby stars. Surveys of high proper motion stars have been used to map the solar neighborhood. LHS 17 is a 16th magnitude high proper motion star moving at an apparent rate of 2.5 arcsec per year with a position angle of 138°. This star's high proper motion has been known since at least 1976 from the Luyten Half-Second Catalogue (LHS). This star was not listed in the 1955 Luyten Five-Tenths Catalogue Catalogue (LFT).


Five archival images were collected from 1955, 1982, 1997, 2008 and 2017. The first image is from an early Palomar survey and is probably a pre-discovery image. The next 3 images are from the DSS archives. I acquired the data for the 2017 image using an iTelescope at Siding Springs Observatory, Australia. The bright field star is HD 17251 mag 7.7.

Image Date Archive Telescope
1 10/22/1955 Palomar1 48" Palomar Schmidt
2 10/15/1982 DSS-1 1.2m UK Schmidt
3 09/27/1997 DSS-2 Red 1.2m UK Schmidt
4 12/22/2008 SDSS DR12 2.5m Apache Point

Four aligned images of LHS 17 moving from left center towards the upper right over a period of 53.2 years.



Proper Motion Calculation

  1. Queried VizieR for a star dimmer than 13th magnitude with a annual proper motion of at least 2.0 mas and at a location covered by Palomar and DSS surveys

  2. Retrieved 2008 image from DSS archives and plate solved along with 2017 image

  3. LHS 17 position determined in 2008 and 2017 images with Astropy daofind function

  4. From the two positions over an 8.88 year span the total motion is 22.09 arcsec, annual Proper Motion is 2.49 arcsec/yr with a position angle of 136.8°

  5. Accepted Proper Motion from the Southern Infrared Proper Motion Survey is 2.488 arcsec/yr with a position angle of 137.9°


Tangential Velocity


Stellar tangential velocities with respect to the Sun are typically 10's of km/s. To convert from proper motion to tangential velocity requires a star's distance derived from parallax. LHS 17 has a parallax of 61.0 mas. Tangential velocity can be calculated from:

  vt = 4.74 * u / p
  vt = 193 km/sec

where:
  u is proper motion in arcsec/year
  p is parallax in arcsecs
  vt is tangential velocity in km/sec