402 research outputs found
Multiperiodic Galactic field RR Lyrae stars in the ASAS catalog
The All Sky Automated Survey (ASAS) monitors bright stars (8 mag < V < 14
mag) south of declination +28 deg. The ASAS Catalogue of Variable Stars (ACVS)
presently contains 50,099 objects; among them are 2212 objects classified as RR
Lyrae pulsating variables. We use ASAS photometric V band data to search for
multiperiodicity in those stars. We find that 73 of 1435 RRab stars and 49 of
756 RRc stars exhibit the Blazhko effect. We observe a deficiency of RRab
Blazhko variables with main pulsation periods greater than 0.65 days. The
Blazhko periods of RRc stars exhibit a strongly bimodal distribution. During
our study we discovered the Blazhko effect with multiple periods in object ASAS
050747-3351.9 = SU Col. Blazhko periods of 89.3 d and 65.8 d and a candidate of
29.5 d were identified with periodogram peaks near the first three harmonics of
the main pulsation. These observations may inspire new models of the Blazhko
effect, which has eluded a consistent theory since its discovery about one
hundred years ago. Long term lightcurve changes were found in 29 stars. We also
found 19 Galactic double mode pulsators (RRd), of which 4 are new discoveries,
raising the number of ASAS discoveries of such objects to 16, out of 27 known
in the field of our Galaxy.Comment: 12 pages, 10 figures, published in MNRA
Pre-discovery and Follow-up Observations of the Nearby SN 2009nr: Implications for Prompt Type Ia SNe
We present photometric and spectroscopic observations of the Type Ia
supernova SN 2009nr in UGC 8255 (z=0.0122). Following the discovery
announcement at what turned out to be ten days after peak, we detected it at V
~15.7 mag in data collected by the All Sky Automated Survey (ASAS) North
telescope 2 weeks prior to the peak, and then followed it up with telescopes
ranging in aperture from 10-cm to 6.5-m. Using early photometric data available
only from ASAS, we find that the SN is similar to the over-luminous Type Ia SN
1991T, with a peak at Mv=-19.6 mag, and a slow decline rate of Dm_15(B)=0.95
mag. The early post-maximum spectra closely resemble those of SN 1991T, while
the late time spectra are more similar to those of normal Type Ia SNe.
Interestingly, SN 2009nr has a projected distance of 13.0 kpc (~4.3 disk scale
lengths) from the nucleus of the small star-forming host galaxy UGC 8255. This
indicates that the progenitor of SN 2009nr is not associated with a young
stellar population, calling into question the conventional association of
luminous SNe Ia with the "prompt" component directly correlated with current
star formation. The pre-discovery observation of SN 2009nr using ASAS
demonstrates the science utility of high cadence all sky surveys conducted
using small telescopes for the discovery of nearby (d=<50 Mpc) supernovae.Comment: 11 pages, 11 figures, 4 tables. Accepted for publication in ApJ on
11/02/201
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