LHS 17 - High Proper Motion Star


Overview

Surveys of high proper motion stars have generated the census of stars in the solar vicinity. Since the proper motion of a star is inversely proportional to its distance from the observer, a high proper motion is a filter for identifying nearby stars. 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, Luyten Half-Second Catalogue (LHS) Catalogue, 1976. This star was not listed in the 1955 Luyten Five-Tenths Catalogue Catalogue (LFT), 1955.


Five images taken in five different epochs are collected: 1955, 1982, 1997, 2008 and 2017. The first image is from an early Palomar survey and may be a pre-discovery image. The next 3 images are from the DSS archives. I acquired the data for the 2017 image using an iTelescope in Mayhill, NM. The bright field star is HD 17251 at mag 7.7.

Image # Obs Date Archive Telescope Years after image #1 Movement from Image #1
1 10/22/1955 Palomar1 Palomar Schmidt
2 10/15/1982 DSS-1 UK 1.2m Schmidt 27.0 67.1 arcsec
3 09/27/1997 DSS-2 Red UK 1.2m Schmidt 41.9 104.2 arcsec
4 12/22/2008 SDSS DR12 Apache Point 2.5m 53.2 132.3 arcsec
5 xx/xx/2017 17" Planewave 62.1 154.4 arcsec

Identification

  1. Queried VizieR for suitable candidate objects at a location covered by earlier DSS surveys. Queried for a star of 14th magnitude or dimmer and a proper motion of 2.0 mas annually or greater. VizieR source catalog.

  2. Aligned images with PixInsight StarAlignment.

  3. Confirmed identification of the transient object by examining the field in SKY-MAP.ORG.

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



Stellar tangential velocities with respect to the Sun are typically 10's of km/s. To convert from proper motion to tangential velocity, one needs to know a star's parallax (and thus distance). LHS 17 has a parallax of 61.0 mas (16.4 parsecs). The tangential velocity of LHS 17 in km/sec can be calculated from:

  vt = 4.74 * u / p

where:
  u is proper motion in arcsec/year
  p is parallax in arcsecs

  vt = 193 km/sec