TRIFFID observations of the cores of the three globular clusters M15, M92 and NGC 6712

Abstract

We present the results of TRIFFID simultaneous V‐ and B‐band observations of the cores of the globular clusters M15, M92 and NGC 6712. A variability search of their dense centres was made feasible through performing post‐exposure image sharpening on the images, increasing the image resolution by a factor of ∼2. The isis implementation of the image subtraction technique developed by Alard & Lupton was then used to detect flux variations in our image sets. We have obtained periods for all observable variables (in our field of view) in NGC 6712 and we have found two new RR Lyrae variables (an RRab and an RRc). We have confirmed three variables in our field of view of the M92. For M15, we detect 48 variables in our field of view, 23 of which are new discoveries. We obtain periods and amplitudes for all variables and classify new ones based on the light‐curve shape, the most significant period and the mean magnitude in the V band. Among the detected RR Lyrae we find 19 RRc, 12 RRab and two RRd types. In the subsequent analysis we find a marked increase in RRc over RRab variables in the core. In a refined procedure to search for fainter objects we find no dwarf novae in our field of view of M15. Simulations performed on the data set to quantify our sensitivity to such objects indicate that an upper limit of 10 dwarf novae (at 92 per cent probability) exist in our field of view. The implications this result has on globular clusters are discussed.

Cluster AgeS Experiment (CASE): deficiency of observed dwarf novae in globular clusters

“…For 16 GCs our survey yielded on average 50 nights per cluster, much more than any survey conducted so far. Past surveys of M92, M15 and of NGC 6712 extended over 10 (independently: Shara, Bergeron & Moffat 1994; Tuairisg et al 2003), 13 and 11 nights (Tuairisg et al 2003), respectively. In total, there are 12 known DNe in seven Galactic GCs.…”

Near-Infrared Observations of RR Lyrae Variables in Galactic Globular Clusters. I. The Case of M92

“…A sizable sample of 60 bright RG stars, including also three candidate variables detected by Walker (1955), were checked for variability by Welty (1985), but none was confirmed variable. During the last few years, the sample of RR Lyrae stars has been investigated more in the optical than in the NIR bands Cohen 1992;Cohen & Matthews 1992;Storm, Carney & Latham 1992, hereinafter SCL;Kopacki 2001;Piersimoni et al 2003;Tuairisg et al 2003). In particular, NIR observations for 3 RR Lyrae stars have been collected by Cohen (1992) and by Storm, Carney, & Latham (1994) to estimate the distance to M92 using the Baade-Wesselink method.…”

The Luminous Erupting Dwarf Nova CV 1 in the Dense Globular Cluster M15

“…The 2 week duration search for dwarf novae in M15 by Ó Tuairisg et al (2003) failed to detect any new candidates. The remarkable result that either zero, one, or at most two erupting dwarf nova can be found in massive globular clusters seems to be holding true.…”

“…This leads to the transfer of mass, via an accretion disk, from the red dwarf to the white dwarf component-in other words, to cataclysmic variables (CVs). However, searches for the many dozens of expected erupting CVs have typically found zero to two dwarf novae in clusters searched from the ground (Shara et al 1994;Ó Tuairisg et al 2003) and with the Hubble Space Telescope (HST ) (Shara et al 1996;Knigge et al 2002).…”