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Preliminary results from the observations of DT Lupus, a newly discovered oscillating Algol binary.

Oscillating Algol stars

All pulsating Algols detected and analysed thus far lie inside the classical 5 Scuti star instability strip very close to the ZAMS (Mkrichian et al. 2002). The authors also adopted the oEA (oscillating eclipsing Algols) designation for mass accreting, pulsating components in Algols. This was to distinguish them from the earlier designation EA/DSCT from the General Catalogue of Variable Stars (GCVS) wherein by default, detached systems with normal [delta] Scui pulsations were included. oEA form a completely separate group of pulsators that differ from 5 Scuti stars but will include Algols with both EA and EB type light curves. The main difference between the two classifications, EA and oEA, is their previous evolutionary life in close binary systems. Rapid Mass Transfer or Accretion (RMT/RMA) evolutionary stages see low mass progenitors of oEA stars accreting a large portion of mass from Roche lobe overflow of the formally massive secondary component. These stars have now evolved rapidly on thermal time scales to higher mass and luminosity. They are presently situated close to the ZAMS on the HR diagram, are of spectral type B--F, and are at a slow mass accretion (SMA) stage in their evolution. SMA maintains a thermal imbalance and ensures a slow evolution along the MS towards higher masses and earlier spectral type. In the mass accretion process they do not follow standard evolutionary tracks of normal MS or post MS 5 Scuti stars.

Furthermore, the changes of the mean density of the gaining star as a result of accretion of matter can affect the pulsation periods and pulsation properties of oEA stars. These changes in periods could be used to estimate mean accretion rates (Mkrichian et al. 2002). The mass transfer/accretion episodes would be initiated by the magnetic activity of the mass losing star. It is yet uncertain though, how the effect, whilst working on dynamic and thermal time scales could affect the pulsation properties and mode selection mechanisms in the gainers on time scales of weeks to years.

Early work by Wood (1950), Kopal (1954), Crawford (1955) and Hoyle (1955) recognised the importance of semidetached configurations in binary stars.

Also of interest is the fact that these stars are known to have changes in frequency amplitude over short periods.

Observations

Observations of OEA stars using personal telescopes (PT) on the outskirts of Johannesburg, South Africa, began in autumn 2011. The principal objective of the campaign is the detection of pulsations in selected antipodean Algol stars. Table 1 lists the program star details.

Hoffmeister first reported the variability of DT Lup in 1943. Horak, Grygar, van Houten et al. (1999) from a least squares fit of seven minima, report the following ephemeris:

Min I = HJD 2 427 897.643([+ or -] 3) + 1.4530891([+ or -] 6) x E

Candidate selection

1. The candidates should display "high" [DELTA]magnitude amplitude, which is important considering the size and sensitivity of the equipment deployed.

2. Observations within the 14>[m.sub.v]>8 band should not be adversely affected by bright moon nights.

Equipment and observations

Here we present B filter data from 2011. The B filter is preferred as pulsation amplitude changes are more obvious than in the V filter. A Starlight Xpress MX716 self-guiding camera was coupled to a pier mounted Meade LX200GPS 30cm (12inch) PT at a light polluted site in Kyalami, on the northern outskirts of Johannesburg, South Africa. Images including the program star were captured to fits files with a field of view (FOV) of ~660 x 600 [arcsec.sup.2] and a resolution of about 110 arcsec [mm.sup.1]. Control of the PT and camera was done using MSB Astro-Art.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

The Computer clock is reset every 4 minutes, automatically via the World Wide Web from Dimension 4 using a local time server.

Image reductions

Astronomical Image Processing 4 Windows (AIP4Win--www.willbell.com/aip/index.htm) was utilised in data reduction. AIP4Win uses two dimensional aperture photometry in the reduction process.

Analyses of reductions

Figure 2 shows DT Lup observed during the evening of HJD 245 5713.2 approaching a secondary maximum. Over this ~ 8 hour observation period three distinct cycles are evident. Running these data through Period04 (Lenz and Breger, 2005) produces a frequency of 8.73 cycles [day.sup.-1] after pre-whitening of the binary orbital period. Figure 3 shows the periodogram of the frequency analysis.

Figure 4 shows DT Lup at primary maximum during the observation as well as a primary minimum calculated by spline fitting. Period Analysis software (Peranso) fits a polynomial to a segment of a light curve by marking a let and right margin cursor. The program calculates the extremum to be located where the gradient of the fitted polynomial = 0. That is, the red vertical line shown in figure 4. The minimum in this instance is calculated at HJD 245 5715.474917 [+ or -] 0.00205.

Investigation of the next closest minimum from the ephemeris given above suggests E = 19144.927 cycles and HJD ([Min.sub.1]) 2455715.58073040. With this preliminary result we cannot confirm a change in the binary orbital period but it is compelling to entertain the thought of a significant change in period through mass transfer.

Conclusion

The preliminary investigation of DT Lup suggests that it is another oscillating eclipsing Algol system. Further observation with a larger telescope is recommended. If this Oscillating Eclipsing Algol is confirmed, the number of these stars thus far detected would swell to just over 20.

[FIGURE 4 OMITTED]

References

Crawford, J., 1955, ApJ, 121, 71

Hoffmeister, C., 1943, Kl. Veroff. Berlin-Ba belsberg, No 27

Horak, T.B., Grygar, J., van Houten, C.J. et al.; 1999; CoSka. 29, 127H

Hoyle, F., 1955, Fronteirs of Astronomy, Harper Collins, New York.

Kopal, Z.: 1954, MNRAS.114. 101K

Lenz, P., Breger, M., 2005, Comm. In Asteroseismology, 146.

Mkrtichian, D.E., Kusakin, A.V., Gamarova, A. Yu.; 2002, ASP Conference Series, Vol. 259, 256

Wood, F.B., 1950, ApJ, 112, 196

C.T. Middleton, Department of Physics, University of Johannesburg, P.O. Box 524, Auckland Park, Johannesburg 2006, South Africa cmiddleton@uj.ac.za
Table 1. Program star details

DT Lup

STAR            DT Lup
SPECTRAL TYPE   AOV C (Simbad)

RA         Dec         HD       TYC           GSC
-2000      (2000)                                           B

14 36 36   -51 24 49   12S0S7   8290-1495-1   03290-01495   9.S

Table 2: Month of observations and integration time, B
Filter Observations 2011

Star     Observing   Integration
         Period      Times

DT Lup   DT Lup      75 seconds
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Title Annotation:observers page
Author:Middleton, C.T.
Publication:Monthly Notes of the Astronomical Society of Southern Africa
Article Type:Report
Date:Oct 1, 2011
Words:1081
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