[vsnet-campaign 1635] TT Ari: "Intermediate-High" Luminosity State Transition and Now Back

[Ivan L.Andronov]

TT Ari: "Intermediate-High" Luminosity State Transition and Now Back


J.N. Yoon (CBNU, Korea), I.L. Andronov (ONU, Ukraine, tt_ari at ukr.net), Y. Kim (CBNU, Korea)

TT Ari has been recently found to be out of the "positive superhump" state, which lasted from 1997 (Skillman et al. , 1998, ApJ, 503 L67; Andronov et al., 1999, AJ, 117, 574) to at least 2004 (Andronov, Ostrova & Burwitz 2004, VSNET-Campaign 1555, http://uavso.pochta.ru/TTAri), by Andronov, Gazeas & Niarchos (2005, VSNET-Campaign 1630, http://uavso.pochta.ru/TTAri2005). The light curve was dominated by quasi-periodic oscillation with a characteristic semi-amplitude ~0.045 mag (VR) (Andronov et al., IBVS 5664). After that, the brightening of TT Ari was reported by Maehara [vsnet-alert 8771].

Here we present a brief report on the "outburst-like" behaviour of TT Ari. It is based on 22 nights of the CCD observations obtained at the 40-cm telescope of the University Observatory, Chungbuk National University, Cheongju, Korea. From October 25 to December 19, 2005, alltogether 6106 data point have been obtained using the R filter with a time resolution 34-70 sec. 

The adopted magnitudes of the comparison star "c" (Shafter et al. 1985, ApJ, 290, 707) are U=12.042, B=11.716, V=11.014, R=10.410, I=9.973 (Efimov et al., IzvCrAO, 1998, 94, 263). The previously published magnitudes of this star (U=11.91, B=11.68, 10.99, Shafter et al. 1985, ApJ, 290, 707; adopted by Goetz 1985, IBVS 2823).
Maehara [vsnet-alert 8771] used "Comp. TYC2 1207.1535.1 V=11.17 B-V=0.65", so the systematic difference of the magnitude of the comparison star is to be taken into account for accurate comparison of the data obtained by various observers. One should recommend to avoid to use the star "d" as the main comparison star because of its very red color B-V=1.15 (Goetz 1985, IBVS 2823), despite it is more close to the variable. 

Detailed study of variability at three detected time-scales will be presented elsewhere after finishing the observational campaign "TT Ari-2005".

The long-term light curve of TT Ari and the control star "d", based on our observations, is presented at http://uavso.pochta.ru/TT2005R.gif
The table of nightly sample mean values of time <t>, magnitude <m_R> and its accuracy estimate sigma are presented in the following table:

<t>-2400000  <m_R>    sigma
53669.16608 10.9975  0.0073
53684.13588 11.1667  0.0033
53685.06281 11.1341  0.0042
53686.14215 11.1767  0.0028
53687.08587 11.1435  0.0031
53692.06316 11.1194  0.0021
53693.09523 11.1228  0.0026
53694.12418 11.1418  0.0029
53695.12250 11.1039  0.0028
53697.03612 11.1090  0.0028
53699.07330 11.0404  0.0028
53701.07125 11.0932  0.0075
53704.21028 10.9180  0.0044
53705.15261 10.8413  0.0035
53707.12664 10.7678  0.0031
53707.90587 10.7859  0.0106
53713.08494 10.4350  0.0040
53715.10349 10.2661  0.0036
53718.95241 10.4005  0.0113
53720.18131 10.3689  0.0082
53722.05972 10.3352  0.0031
53724.10434 10.6694  0.0039

To this table, one nightly mean in the filter V may be added in the same format:
<t>-2400000  <m_V>    sigma
53683.22808 11.4050  0.0057

The light curve may be splitted into at least 4 parts:
approximate standstills in the intervals 
HJD 2453684-701 ("intermediately faint state" <m_R>= 11.123(1)) ,
HJD 2453713-722 ("bright state" <m_R>= 10.341(3)) ,

nearly linear rise
HJD 2453704-715 (the slope dt/dm=15.87(11)) ,
and fall
HJD 2453721,724 (the slope dt/dm=4.95(7), but two recent nights only)

The maximum amplitude of this outburst-like event is 0.9 mag (R).