GAIA14AAE a very interesting hydrogen-deficient compact binary

Gaia14aae (ASASSN-14cn) was detected by Gaia on 2014-08-11, during an outburst.
Low to intermediate resolution spectra taken at the 4.2m William Herschel Telescope on La Palma, over the nights of 13-15 October 2014, using ISIS+R300B/R158R and ACAM+V400, show a double peaked He emission lines at z=0, with no H.
 

Such spectra allow us to classify Gaia14aae as a AM CVn system, a pretty rare class of object (see Atel 6593).
AM CVn systems are ultra-compact, semidetached, white dwarf binaries with periods ranging from 5 to 65 minutes. The prototype (with an orbital period of 17 min.) was discovered in 1967 (Smak J., 1967, Acta Astron., 17, 255).
Bohdan Paczynski (1967, Acta Astron., 17, 287) proposed that such a system was a very short period binary with a degenerate, helium-rich donor in a very tight orbit.
The theory of general relativity predicts that such a system would emit gravitational waves and loose angular momentum. This drives mass transfer from the lower-mass (bigger)hite dwarf to its companion. Despite the loss of angular momentum, the redistribution of mass makes the binary orbit widen and thus the orbital period increasing.
Since the 1960s only a few tens have been discovered, with periods up to 65 minutes. In the meantime the theoretical models of how to bring two white dwarfs (or white dwarf like objects) in such close orbits have developed. The small number of known systems, however, makes it difficult to test the viability of the different models.
Photometric data (98 frames in the Gunn g band, with exposure times of 420, 300 and 30 sec) acquired on October 24, 2014, with BFOSC at the 1.5m G.D. Cassini telescope in Loiano (Italy)

and CBA data by E. de Miguel

show that Gaia14aae is an eclipsing system, with a 49.7 min. period, i.e. the third known eclipsing AM CVn (a possible SN Ia progenitor candidate).
BFOSC data have been also used to create this time lapse, shrinking 88 min into a 21 sec movie, that very clearly shows the deep eclipse.
 

PIs: Gisella Clementini, Lukasz Wyrzykowsky

Observers: H. Campbell, K. Rybicki, P. Wielgorsky, G. Altavilla, R. Gualandi

Reduction and observing strategy S. Hodgkin