MBCAA Observatory

EH Lib: 2007 follow up

Observed: 24 Apr, 7, 12 July 2007

Michel Bonnardeau
16 Nov 2007

Abstract

Time-series of this DSCT pulsating star with a period of 2.1h are presented and compared with 2004-2005 observations.

Introduction

EH Lib is a pulsating star of the DSCT (delta Scuti) type. Stars of this type have radial and non radial pulsations. The period of the pulsations of EH Lib is 2.12 hours.

I already observed this star in 2004-2005; these new time-series are to assess the pulsational stability.

Observations

The observations were carried out with a 203mm f/6.3 SC telescope, a V filter (a Rc filter in 2004-2005) and a SBIG ST7E camera (KAF401E CCD). 318 images were obtained, each exposure is 60s long.

The comparison star is TYC4987.00657/1 with a V magnitude of 9.796, computed from the Bt and Vt magnitudes owing to Mamajek et al (2002) & (2006). There are 3 check stars: K=GSC4987-00415 with a measured magnitude of 11.209 and a standard deviation of 0.013, K1=GSC4987-00180 (12.206+/-0.023), K2=GSC4987-00262 (11.936+/-0.027).

An example of a light curve:

Red: EH Lib; magenta, dark, blue: the K star shifted by -1 mag, K1 shifted by -1.7, K2 shifted by -1.2, respectively. The error bars are +/- the 1 sigma statistical uncertainties.

All the light curves are HERE.

Pulsational stability

According to the GCVS the ephemeris for the pulsation is:
t = 2433438.6082 (6 Jun 1950) + 0.0884132445*E

This yields the phase plot:

The pulsation is 0.035 period or 4mn late from the ephemeris.

This can be compared with my 2004 and 2005 observations (Rc filter):

Red: these 2007 observations (V filter);
Green: 2005 (Rc filter) shifted by -0.95 mag;
Blue: 2004 (Rc filter) shifted by -1.1.

There may be some hint that the pulsation is slowing down (or that the period needs to be refined), but no hard evidence.