Discovery of Stellar Duplicity of TYC During Asteroidal Occultation by (191) Kolga

Transcription

1 Page 162 Discovery of Stellar Duplicity of TYC During Asteroidal Occultation by (191) Kolga Brad Timerson, IOTA North American Coordinator T. George, observer and lead author J. Bean, T. Blank, J. Bardecker, D. Dunham, J. Dunham, B. Gimple, P. Maley, S. Anthony (RECON ), C. Wiesenborn (RECON), T. Hunt (RECON), R. Sumner, and W. Thomas, observers Abstract: An occultation of TYC by the asteroid (191) Kolga on 2018 February 9 showed this star to be a double star. Both components of the double star were occulted as recorded by seven observers and one or the other component of the double star was occulted as recorded by three observers. There were five miss observations. The separation of the two components is ± arcseconds at a position angle of ± 3.5 degrees. The magnitude of the primary component is estimated to be v ± The magnitude of the secondary component is estimated to be v ± Observation On 2018 February 9, fifteen observing stations across the western United States observed the asteroid (191) Kolga occult the star TYC See Figure 1 for the path map of the event. All of the fifteen stations collected video data for the event. Of the fifteen stations that collected video data, seven observed two separate drops in brightness, neither of which singularly had a mag drop as large as predicted, indicating a double star (see Figures 4-13). One site (Anthony) had only a single drop in brightness (see Figure 2) that was consistent with observation of the primary star only. sites (Bardecker and Wiesenborn) had only a single drop in brightness (see Figure 2 ) that was consistent with observation of the secondary star only. Five other sites had a miss. All recorded occultation times and data from the observers can be found in archived IOTA records for the event. The successful observations were made by the observers located at the sites and with the equipment shown in Table 1. The result of each observation is also shown. The target star is magnitude v GaiaDR2 from the Occult4 [1] database. The asteroid magnitude as predicted by Occult4 was 13.5 (v). The combined magnitude of asteroid and star was calculated to be (v). The expected magnitude drop at occultation was 1.56 magnitudes (originally listed as 1.7 based on star magnitude of 12.1). The star is not listed in the Fourth Interferometric Catalogue, nor is it listed in the Washington Double Star catalog. There were no previous catalogued occultations of this star lunar or asteroidal. Analysis The observations were analyzed in the standard manner described by IOTA [2]. The finished plot of the double star fit to the data including a fit to the ellipsoid of best fit is shown in Figure 6. The double star has a separation of ± arcseconds at a position angle of ± 3.5 degrees. Of the data sets that recorded the occultation, seven observers recorded both with magnitude drops suitable for calculating the stellar component magnitudes. Using the light curve data from the seven positive observers of both, the brightness measurements derived using ROTE [3], and the Magnitude calculator routine in Occult4 (Method 3 Magnitudes from light curve values), the brightness of the double star components based on a combined brightness of (GaiaDR2) was calculated. The results are shown in Table 2. Based on the average magnitude error estimates for the two components shown in Table 2, the ABAB [4] event sequence was selected as the correct sequence. (Text continues on page 170) RECON: Research and Education Collaborative Occultation Network

2 Page 163 Figure 1. Occultation path (top) and occultation sites in southern Nevada and Phoenix, Arizona area.

3 Page 164 Figure 2. Occultation sites. Nevada, California, and Oregon. Table 1. Observer(s), site locations, equipment, methods, and results Chord Observer Location/City/Site State Telescope Type Telescop Dia (cm) Recording+ Timing Longitude Latitude 1 Anthony, S. Klamath Falls OR SCT 30cm Video+GPS m One event 2/3 Dunham, D. & J. Deer Cr Trhd-Sta 4 AZ Reflector 25cm Video+GPS m 4/5 Dunham, D. & J. Rio Verde-Sta 3 AZ Refractor 12cm Video+GPS m 7/8 Dunham, D. & J. Mesquite SA-Sta 2 AZ Refractor 12cm Video+GPS m 9/10 Dunham, D. & J. Sycamore Cr-Sta 1 AZ Reflector 25cm Video+GPS m 11/12 Maley, P. Carefree AZ SCT 28cm Video+GPS m 13/14 George, T. Scottsdale AZ SCT 30cm Video+GPS m 15/16 Blank, T. Fountain Hills AZ SCT 35.5cm Video+GPS m 17 Bardecker, J. Silver Springs NV SCT 20cm Video+GPS m One event 18 Wiesenborn, C. Boulder City NV SCT 30cm Video+GPS m One event 19 Thomas, W. Florence AZ SCT 28cm Video+GPS m Miss Elevation 20 Hunt, T. Yerington NV SCT 30cm Video+GPS m Miss 21 Collins, M. Chandler AZ Other(?) 32cm Video+GPS m Miss 22 Sumner, R. Dayton NV SCT 20cm Video+GPS m Miss 23 Gimple, B. Greenville CA SCT 28cm Video+GPS m Miss 24 Bean, J. Carson City NV SCT 30cm Video+GPS m Miss Result

4 Page 165 Table 2 ABBA ABAB Site MagA MagB MagA MagB Dunham Dunham Dunham Dunham George Maley Blank Average Error where A = first D occultation; B = second D occultation Figure 3 Chord 1 Klamath Falls light curve shown before and after block integration and normalization. Only one component of double star occulted.

5 Page 166 Figure 4 Chord 2/3 Dunham Station 4 both components of double star occulted.. Figure 5 - Chord 4/5 Dunham Station 3 -- light curve shown before and after block integration and detrending. Both components of double star occulted.

6 Page 167 Figure 6 - Chord 7/8 Dunham Station 2 -- light curve shown before and after block integration and detrending. Both components of double star occulted. Figure 7 - Chord 9/10 Dunham Station 1 -- light curve shown before and after normalization to nearby secondary star. Both components of double star occulted.

7 Page 168 Figure 8 - Chord 11/12 Maley, Carefree, AZ -- light curve shown before and after block integration Figure 9 - Chord 13/14 George, Scottsdale, AZ Figure 10 - Chord 15/16 Blank, Fountain Hills, AZ

8 Page 169 Figure 11 - Chord 17 Bardecker, Silver Springs, NV. Light curve shown before and after block integration and normalization. Only one component of double star occulted. Figure 12 - Chord 18 Wiesenborn, Boulder City, NV -- Light curve shown before and after block integration and detrending to nearby secondary star. Only one component of double star occulted.

9 Page 170 Boulder City, NV Figure 13 (191) Kolga occultation of TYC Profile plot using both stars of double star system and showing the separation and position angle of the double star system [6]. (Continued from page 162) The ABAB sequence resulted in the lowest stddev error compared to the ABBA sequence. The magnitude of the two component stars was derived from the Occult4 analysis are estimated to be ± 0.05 V primary (brighter) star and ± 0.05 v secondary (dimmer) star. The event was a BABA [5], with the secondary occulted first, then the primary. Based on the data presented in this report, the double star characteristics are shown in Table 3. References 1. Herald, D. Occult4 software, (2015) Magnitude additions and magnitude drop calculations. Unpublished profile routine using a least squares fit of an ellipse to the observed occultation chords as projected onto a moving reference frame on the fundamental plane. Star Coordinates (J2000) Mag A Mag B Separation (arcsec) Position Angle (deg) Table 3 TYC TGAS UCAC UCAC PPMXL E+18 Spectral type not found RA Dec ± 0.05 v ± 0.05 v ± ± 3.5

10 Page New Double Stars from Asteroidal Occultations, , Dave Herald, Canberra, Australia, Journal of Double Star Observations, Volume 6 Number 1 January 1, ROTE R-Code Occultation Timing Extractor Presentation at the 2013 Annual IOTA Meeting, October 4-6, 2013; Toronto, Ontario, Canada. NA/2013Meeting/R-OTE%202013%20IOTA% 20Conference.pdf 4. In this context: A=first star occulted and B=second star occulted, without reference to which star is brighter. 5. In this context: B=the secondary (dimmer) star and A=the primary (brighter) star. 6. Note: as of the date of preparation of this paper, the PA and Sep reported by the authors does not agree with the PA and Sep reported in the IOTA Occult4 database. This is due to the Occult4 database plot reappearance data for Chord 2 given Zero Weight. The authors gave the Chord 2 reappearance equal weight to all other observations.