BL Telescopii

BL Telescopii

A visual band light curve for BL Telescopii, plotted from data published by van Genderen (1983)[1]
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Telescopium
Right ascension 19h 06m 38.10893s[2]
Declination −51° 25′ 03.2131″[2]
Apparent magnitude (V) 7.09 - 9.08[3]
Characteristics
Spectral type F4Ib+M[3]
Variable type Algol
Astrometry
Radial velocity (Rv)+98.57[4] km/s
Proper motion (μ) RA: -6.876[4] mas/yr
Dec.: 0.525[4] mas/yr
Parallax (π)0.6223 ± 0.0410 mas[4]
Distance5,200 ± 300 ly
(1,600 ± 100 pc)
Absolute magnitude (MV)−4.5[5]
Orbit
Period (P)778.0 d[6]
Eccentricity (e)0.31±0.02[6]
Inclination (i)~68[5]°
Semi-amplitude (K1)
(primary)		19.3±0.5[6] km/s
Details
Radius64[4] R☉
Luminosity3,225[4] L☉
Temperature5,438[4] K
Other designations
CD−51 11917, HD 177300, HIP 93844
Database references
SIMBADdata

BL Telescopii is a multiple star in the constellation Telescopium.[2] An Algol-like eclipsing binary, the star system varies between apparent magnitudes 7.09 and 9.08 in just over 778 days (2 years 48 days),[3] which is generally too faint to be seen with the unaided eye.[7] This is mainly due to the system being an eclipsing binary (that is, one star passing in front of the other star and resulting in a change in brightness). The eclipse itself dims the star by two magnitudes and lasts around 104 days.[6]

Dutch astronomer Willem Jacob Luyten noted this star to be variable in 1935. Minima were retrospectively identified in old photographic plates from 1913 and 1919, and then observed by Howarth in 1936. Initially thought to be an R Coronae Borealis variable, its true nature as an eclipsing binary became clear in the 1940s.[6]

The primary component is a yellow supergiant, whose spectral type has been calculated as either F5Iab/b or F4Ib. It is intrinsically variable, varying in brightness by 0.02 magnitude. It has pulsations of two periods, 92.5 days and 64.8 days in length. It has been classified as a UU Herculis variable—a class of yellow supergiant with semiregular variability.[8] These stars are thought to have affinities with Cepheid variables and lie near the instability strip on the Hertzsprung–Russell diagram. The secondary was identified as an M-type star from TiO (titanium oxide) absorption bands visible during the eclipses.[6]

The BL Telescopii system lies outside the galactic plane and has a high space velocity; it is a runaway star.[5]

  1. ^ Cite error: The named reference Genderen was invoked but never defined (see the help page).
  2. ^ a b c "BL Telescopii -- Eclipsing binary of Algol type (detached)". SIMBAD Astronomical Database. Centre de données astronomiques de Strasbourg. Retrieved 14 July 2014.
  3. ^ a b c Otero, Sebastian Alberto (31 July 2006). "BL Telescopii". AAVSO Website. American Association of Variable Star Observers. Retrieved 14 July 2014.
  4. ^ a b c d e f g Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  5. ^ a b c Van Genderen, A. M.; Glass, I. S.; Feast, M. W. (1974). "The long period, high latitude, eclipsing system V748 Cen (= Cen X-4?) and BL Tel". Monthly Notices of the Royal Astronomical Society. 167 (2): 283–298. Bibcode:1974MNRAS.167..283V. doi:10.1093/mnras/167.2.283.
  6. ^ a b c d e f Feast, M.W. (1967). "The supergiant eclipsing system BL Telescopii". Monthly Notices of the Royal Astronomical Society. 135 (3): 287–304. Bibcode:1967MNRAS.135..287F. doi:10.1093/mnras/135.3.287.
  7. ^ Bortle, John E. (February 2001). "The Bortle Dark-Sky Scale". Sky & Telescope. Sky Publishing Corporation. Archived from the original on 31 March 2014. Retrieved 14 July 2014.
  8. ^ Zsoldos, E. (1994). "The pulsations of yellow semi-regular variables II. The F supergiant in the high-latitude binary BL Telescopii". Astronomy and Astrophysics. 286: 870–74. Bibcode:1994A&A...286..870Z.