Variable Stars - T Ori
Type X Orionis type Click for lightcurve X Orionis stars are collectively known in the literature as UXors. Subgroup of Young Stellar Objects that show irregular variations with a wide range of amplitudes from barely detectable to more than 4 mag in V. Most of them are Herbig Ae/Be stars but there are some T Tauri stars with later spectral types also showing the same behaviour. Large-amplitude variability is confined to stars with spectral types later than B8. There are two principal components: (1) irregular variations on time-scales of days around a mean brightness level that changes on a much longer time-scale (typically years), sometimes in a quasi-cyclic fashion, and (2) occasional episodes of deep minima, occurring at irregular intervals but more frequently near the low points of the brightness cycles. UXors show increased polarization when the optical light of the star becomes fainter (presence of clumps in our line of sight) and redder, while in extreme visual minima there is a color reversal. Currently mixed among the ISA, INA or INSA classes in the GCVS. AAVSO Alert 490: August 30, 2013 Dr. William Herbst (Wesleyan University) and Rachel Pedersen (Bates College) have requested AAVSO assistance in monitoring the Orion variable T Ori in support of spectroscopy they will be obtaining during September 2013. AAVSO nightly coverage (visual or electronic, not time series) of this star is crucial throughout the month of September. Dr. Herbst writes: "T Ori is one of the first variable stars discovered, varies by up to several magnitudes, and remains a mysterious object. The cause of its variability is not fully known more than a century after its discovery!  To help address this issue, my student Rachel Pedersen and I will be obtaining high resolution spectra with the SMARTS 1.5m telescope at the Cerro Tololo Interamerican Observatory in Chile during the month of September, 2013. We hope to observe spectral changes accompanying the brightness variations that will shed light on their cause. It is critical that we be able to assign a magnitude to each spectrum. Amateur astronomers could make a terrific contribution to this project by more intensively monitoring the star during September. ""For visual observers: Estimates of the brightness using the AAVSO charts will be helpful. Since the star changes brightness by up to several magnitudes, an accuracy of 0.1 or even 0.2 mag as can be achieved by careful visual observers will be sufficient. Observations made with care by experienced observers will be most helpful to us.  ""For CCD observers: V magnitude or even unfiltered observations will be most useful. If colors can be obtained (e.g. UBVRI) they could be helpful, but we primarily need a magnitude estimate."
Hills Observatory: 1 January 2013 to 2 December 2018
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