Unveiling CI Hyi as a symbiotic system
Active Dates: Sept. 10, 2024 – Sept. 10, 2025
Abstract:
A significant population of asymptotic giant stars (AGBs) have been known to be sources of X-ray emission (X-AGB). A characteristic that indirectly proves the presence of stellar companions. Depending on the properties of the X-ray emission two types of companions have been proposed: a main-sequence star or a compact object such as a white dwarf (WD). In the latter case, the systems is known as a symbiotic star. Recent analysis of the X-ray properties of X-AGB stars show that there seems to be a hidden population of hidden symbiotic systems. Here, we propose to obtain photometric following of one of the most X-ray bright X-AGB, CI Hyi. In combination with high-resolution spectra from the ARAS team, we will be able to peer into the origin of one of the most unknown X-AGB systems. A campaign is underway over the next several months; AAVSO observers are requested to obtain BVRI photometry as detailed below.
Justification:
X-ray observations have been crucial to unveil the binary companions of evolved stars such as those of the asymptotic giant branch (AGB). For decades, the origin of X-ray-emitting AGB stars (X-AGB) have been debated. Attributing the production of the X-ray emission to accreting main sequence stars or to the presence of a compact object such as a white dwarf. The laters, its referred as a symbiotic system (AGB+WD). Although it has been argued that there is a clear separation in X-ray luminosity between these two types of objects, recently, Guerrero et al. (2024, arXiv:2407.10552, accepted to A&A) the population of X-AGB stars detected by eROSITA and compared them to the properties of symbiotic systems. One of the main conclusions is that there is not a clear separation between the two types of sources. Consequently, a better characterization using other wavelengths to search for the companions of AGB stars is most needed. We propose to observe CI Hyi with bands V, B, I and R using the AAVSO team to unveil the optical properties of one of the most X-ray bright X-AGBs. In fact, Guerrero et al. (2024) suggested that its X-ray properties are in agreement with those of a symbiotic system. We have started a campaign to obtain optical spectra of CI Hyi every week using the international team of the ARAS database, which consists of an international program to obtain spectra of variable stars. The optical spectra of CI Hyi will confirm (or invalidate) the status of this object as a symbiotic system. The combination of the proposed V, B, R and I photometry with the high-resolution spectra obtained with the ARAS team will result in an unprecedented characterization of CI Hyi.
Requested Data Types:
Photometry
Targets
| Name | Magnitude | Variability Type | Photometry Notes | Spectroscopy Notes |
|---|---|---|---|---|
| CI Hyi | 9.30 | ZAND:+LB |
Cadence: Nightly Precision: 50 |
Not Requested |
Spectroscopy Lines:
No spectroscopy lines provided
Photometry Filters:
B (Johnson), V (Johnson), R (Cousins), I (Cousins)
Comparison Stars:
Finder charts with comparison stars are available via the AAVSO Variable Star Plotter (VSP, https://apps.aavso.org/vsp/).
Co-Authorship
Observers are not eligible for co-authorship.
Additional Observer Input:
Observers need to be careful not to saturate their camera when observing this bright target, and should stack images as necessary to reduce scintillation. Unfiltered photometry (CV, CR) is not requested for this campaign. Tricolor Blue/Green/Red observations may be useful, but priority in analysis will be given to BVRI. Finder charts with comparison stars for CI Hyi may be created using the AAVSO Variable Star Plotter (https://apps.aavso.org/vsp).
Additional Submission Location:
None requested.
Notes:
No public notes