MBCAA Observatory

V1356 Aql mystery

Observed: 8, 12, 29 Aug 2005

Michel Bonnardeau
14 Sept 2005
Updated: 16, 29 Sept 2005

Abstract

I observe flat light curves for this RR Lyrae star.

Introduction

In the GCVS V1356 Aql is listed as a RR Lyrae (a pulsating star), with the ephemeris:
period=0.324d
time of maximum: 2,443,698.607 (9 July 1978)
The amplitude of the pulsation: 0.2mag.

Observations

The observations were carried out with a 203mm f/6.3 SC telescope, B and V filters used alternatively in a filter wheel and a SBIG ST7E camera (KAF401E CCD). 60 images were obtained with the V filter, 64 with the B. Each exposure is 200s long. Example of an image:

Image made with a V filter. The yellow square is for the comparison star, the blue ticks are for the check star, V1356 Aql has the purple circle.

V1356 was observed over 3 sessions that span a complete period, the phase (between 0 and 1) being computed from the GCVS ephemeris:

Green: V filter observations, Blue: B filter observations.

The comparison star is Tycho-2 5150-00974 with the Johnson magnitudes B=12.248 and V=11.552, computed from the Tycho B and V magnitudes using Mamajek et al (2002). The uncertainties on the Tycho-2 magnitudes are +/-0.243 for Bt, +/-0.183 for Vt. The check star is GSC 5150-00022 with the measured magnitudes B=13.882 (standard deviation 0.072) and V=12.703 (0.014).

The resulting light curves, for V1356 and the check star (K), are the following:

Green: V magnitudes, Blue: B magnitudes minus 0.3. The error bars are +/- the 1-sigma statistical uncertainties.

Green: V magnitudes, Blue: B magnitudes minus 0.7.

V1356 Aql appears to be constant, with V=10.525 (standard deviation 0.009) and B=10.972 (0.019).

Discussion

The references of the GCVS to V1356 Aql are numbered 00470 and 01187:

00470: Hoffmeister (1935) is the discovery paper. The star was called 121.1935 Aql and its coordinates are in agreement with the 2000.0 coordinates of the GCVS. Its detection is reported as difficult;

01187: J.F. Le Borgne (1979) GEOS NC 218. In the GEOS database for RR Lyrae, there is a single visual observation of the time of maximum, which is reported in the GCVS.

V1356 Aql was observed by the ASAS and SkyDOT/ROTSE-I/NSVS surveys:

ASAS: 690 measurements (A, B grade) from 11 Mar 2001 to 17 Sep 2005, in the V band. The results are at http://www.astrouw.edu.pl/cgi-asas/asas_variable/194659-0204.6,asas3,0,0,500,0,0. They are compatible with the star being constant, with a standard deviation of 0.02 mag.

SkyDOT/ROTSE-I/NSVS: 147 measurements from 6 Apr 1999 to 14 Mar 2003. The results are at http://skydot.lanl.gov/nsvs/star.php?num=14156874&mask=32004. They are also compatible with the star being constant, with a standard deviation of 0.028 mag.

V1356 Aql was discussed on the AAVSO-discussion group on 14-16 Sep 2005, and J.F. Le Borgne explained that the GEOS observations were only an internal publication that should not have been released.

I conclude that V1356 Aql is definitively not a RR Lyrae, and is almost certainly a constant star.