EH Lib regular pulses
Observations: April-May 2004, March-April 2005
Michel Bonnardeau
Updated: 5 November 2004
Revised: 18 January 2005
Updated and revised: 30 June 2005
Updated: 16 Nov 2007
Abstract
The pulsating star EH Lib was observed and 15 pulses were measured. They are in phase with the 55-year old ephemeris of the GCVS (may be late by 2 or 3 mn only).Introduction
EH Lib is a pulsating star of the DSCT type (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.Observations
EH Lib was observed over 8 sessions from 25 April 2004 to 5 April 2005 with a 203 mm f/6.3 SC telescope, a SBIG ST7E camera (KAF401E CCD) and a Rc filter. 869 images were obtained. The exposures are all one minute long.
For the differential photometry, 3 comparaison stars were used:
and 2 check stars:
An example of an image is here.
Exemple of a light curve: EH Lib is in red, the K star is green and 0.7
is substracted to the magnitudes, the K1 star is brown and 1.8 is substracted.
The data are heliocentrically corrected.
The error bars are +/- the 1-sigma statistical uncertainties.
All the light curves are here.
Analysis
15 pulses are observed. There are at (in HJD-2453000):
| 121.523 +/- 0.002 | 121.610 +/- 0.0015 | . |
| 142.386 +/- 0.002 | 142.475 +/- 0.002 | 142.563 +/- 0.002 |
| 143.358 +/- 0.005 | 143.447 +/- 0.008 | 143.533 +/- 0.002 |
| 144.418 +/- 0.0015 | 144.508 +/- 0.002 | 144.598 +/- 0.003 |
| 145.569 +/- 0.0015 | . | 149.546 +/- 0.0015 |
| 446.616 +/- 0.002 | 446.705 +/- 0.002 | . |
According to the GCVS, the ephemeris for the times of the pulses is:
t = 2433438.6082 + 0.0884132445*E
in HJD where E is a pulse number. The date of this ephemeris is 6 June 1950.
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The O-C diagram shows that the pulses are about 2 or 3 mn late from
the 55-year old ephemeris.
This suggests that the star pulses very regularly, with a precision of about 10^-7
or 3 s/yr.
When the data are folded along the period, the following light curve is obtained:
Blazhko effect: according to Karetnikov & Medvedev (1979), EH Lib shows the Blazhko effect with a period of 6.57 h and an amplitude of 0.13 mag in the B and V light, in the 1974-1978 period. I do not see this effect: in the Rc light, the amplitude is smaller than 0.05 mag, at the time of my observations.
Reference
Karetnikov V.G., Medvedev Yu.A. (1979) IBVS 1537.
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