Far-UV detection of the low-mass companion responsible for Betelgeuse's long secondary periodThe approximately 2100-day cycle of variability exhibited by the nearby red supergiant Alpha Orionis, popularly known as Betelgeuse, has become the subject of scrutiny after Betelgeuse's sudden, 1.6 V-mag brightness drop in late 2019. The nature of this 2100-day periodicity is closely tied to Betelgeuse's time-until-explosion: if it is the fundamental mode (FM), the star might be close to becoming a supernova. Recent studies, however, have converged instead on the conclusion that the 2100-day variability cycle is actually a Long Secondary Period, or LSP. The origins of the LSP phenomenon are unknown, but consensus is building that LSPs are caused by low-mass companions around the star. Since late August of 2024, two independent studies have proposed such an orbital companion, alpha Ori B, as the cause of Betelgeuse's LSP. The combination of photometric, radial velocity, and astrometric observations indicates a minimum mass of either 0.6 or 1.2 solar mass, and a separation of 2.4 stellar radii from Betelgeuse, which makes direct detection of the companion challenging due to an expected luminosity contrast of >10^4. However, by exploiting the strategic timing of maximum orbital separation occurring on Dec 6, 2024, this observational campaign proposes to find alpha Ori B via far-UV excess, using STIS with the E140M grating. This campaign will yield either the direct discovery of the hidden companion or provide an important constraint on the mass of alpha Ori B, shedding light on the nature of the LSP phenomenon and massive star multiplicity. An additional outcome will be the benchmarking of the chromospheric properties of our nearest RSG.The target will be suitable for observation during the time frame of November 6, 2024 to January 6, 2025, when alpha Orionis B is most likely to be detected. The optimal date of observation, corresponding to maximum orbital separation between Betelgeuse and the companion from our vantage point, is December 6th.
We divide four orbits across four visits, one orbit per visit. We do not require the visits to be consecutive, but it is helpful if they take place close in time.
Into a single orbit, we fit one imaging acquisition on Betelgeuse (alpha Ori) and two 1000-second science exposures.
From each acquisition, we pivot 0.084 (-0.084) arcsec in x and 0.084 (-0.084) arcsec in y. Each visit has one pointing, tiling Betelgeuse in a 2x2 square with the 0.2x0.2 slit.
No special orientation is required.
No background requirements.
This campaign does not require coordination with any other observations, but it will supplement observations from Chandra scheduled around December 9th, 2024.Prof. Meridith Joyce is an assistant professor at the University of Wyoming, jointly appointed in the department of Physics and Astronomy and School of Computing. She is a world expert in 1D stellar evolution and pulsation modeling and the lead author of the first study on Betelgeuse (2020) that used Betelgeuse's periodicities to constrain the star's present-day evolutionary state. She is the PI of a TESS Cycle 7 GI proposal.
Dr. Jared A. Goldberg is a Flatiron Research Fellow at the Flatiron Institute's Center for Computational Astrophysics. He is an expert in the structure and evolution of massive stars and their circumstellar envelopes, leveraging both 1D and 3D modeling. Along with Dr. Joyce and Dr. Molnar, he led the analysis which first predicted the companion to alpha Ori, which is the target of this proposal.
Dr. Laszlo Molnar is a senior research fellow at Konkoly Observatory of the HUN-REN CSFK in Budapest. He is an expert on space-based photometry, stellar pulsations, and asteroseismology, and was the PI of multiple Kepler K2 observing proposals.
Dr. Anna O'Grady is a McWilliams Fellow at Carnegie Mellon University. She is an expert in optical and infrared data analysis and has extensive experience analyzing high resolution stellar spectra.
Dr. Brendan O'Connor is a McWilliams Fellow at Carnegie Mellon University. He is an expert in X-ray, optical, and infrared data analysis with extensive experience in the analysis of HST data, in particular ACS and WFC3. He is currently PI of two active HST programs and Co-I on four other active programs, as well as numerous other programs in past cycles.
Prof. Katie Breivik is an expert in binary population modeling. She will help to place the constraints made from the HST observations in the context of other Galactic populations of massive star hosting binaries and the uncertain models for how they interact and form stellar remnants.
Prof. Maria Drout is an expert in observations of both supernova and stars. She has PI'ed multiple HST proposals requesting UV observations of binary star systems.
Dr. Christian Johnson is a Principal Staff Scientist at STScI and an expert in globular cluster spectroscopy, stellar populations, and large sample photometric analyses. Dr. Johnson has published extensively in fields related to globular cluster abundance patterns as well as the chemical composition of bulge field stars. Dr. Johnson is also the co-PI for the Blanco DECam Bulge Survey, which imaged >200 square degrees of the Galactic bulge using the ugrizY DECam filters. Dr. Johnson is the sole author of that project's PSF photometry pipeline.
Dr. Annalisa Calamida is STScI scientist and the WFC3/HST deputy branch lead. She is an expert in photometric calibration and reduction techniques. She is an expert of stellar populations, stellar evolution and variable stars. She is co-author of the article on "Recommendations for optimizing rapid ultraviolet HST observations of gravitational wave optical counterparts," Strolger et al. 2020, arXiv2002.09392.
Prof. Max Moe is an assistant professor at the University of Wyoming who specializes in the formation and evolution of binary stars. He is an expert on statistics and detection methods of binary stars across the HR diagram, including fitting composite spectral energy distributions across UV, optical, and IR wavelengths.Stellar Physics and Stellar Types0falseSUPPORTEDSTARSUPERGIANT OThis object was generated by the targetselector and retrieved from the SIMBAD database.
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