CBA Center for Backyard Astrophysics

(click figures for larger versions)

XTE J1118+480 Figure 1.
XTE J1118+480 Figure 1.

Figure 1. Power spectrum of the 30-night CBA light curve of XTE J1118+480 in unfiltered ("pink") light. A strong signal at 5.856(4) c/d appears; there is no strong evidence of period or amplitude change during the month (April 2000). The little peaks at very low frequency arise from uncorrected differential extinction, which is very hard to eliminate at such low signal strengths (~0.01 mag).

XTE J1118+480 Figure 2.
XTE J1118+480 Figure 2.

Figure 2. Mean light curve of the 5.853 c/d (0.17085 d) signal. A perfect sinusoid within measurement limits. However, it is noteworthy that all individual-night light curves show vastly more scatter, up to ~0.4 mag. The reason is that the star flickers violently on timescales of a few seconds or faster. Longer integrations smooth over this flickering, which - remarkably! - does not seem to extend to much lower frequencies.

XTE J1118+480 Figure 3.
XTE J1118+480 Figure 3.

Figure 3. Light curve in unfiltered light (3500-9000 A) at 6 s time resolution with the MDM 1.3 m telescope. Violent variations are evident, and unresolved at this time resolution (the measurement error is only 0.02 mag/point). But the flickering power drops to essentially zero at lower frequency, which is why long integration times can average over dozens of flickers and achieve good signal-to-noise in this "noisiest star in the Universe".

XTE J1118+480 Figure 4.
XTE J1118+480 Figure 4.

Figure 4. The 10-s quasiperiodic oscillation in the UMa transient. Upper frame, average power spectrum from 36 12.5 minute runs with a 3.1 s cycle time (1 s integration, 2.1 s readout) during April 30-May 3. Lower frame, log-log power spectrum after smoothing. All data from CBA-East (Dave Skillman, 66 cm f/2.9 telescope). This signal appears to be of ~0.15 mag amplitude --- the cause of the great scatter in the high-speed light curves!

The CBA "UMa Transient" Cabal
Joe Patterson - CBA-New York
Bob Fried - Braeside Observatory
Dave Harvey - CBA-Tucson
Lew Cook - CBA-California
Gianluca Masi - CBA-Italy
Jonathan Kemp - CBA-Oracle
James Hannon - CBA-Connecticut
Denis Buczynski - Condor Brow Observatory
Tonny Vanmunster - CBA-Belgium
Lisa Pidgley, Pierre Maxted, Sofia Araujo-Betancor - Southampton Univ.
Rudolf Novák - Nicolas Copernicus Observatory (Brno)
Dave Skillman - CBA-Maryland
Brian Martin - CBA-Alberta

CBA Finding Chart