Two Be or Not Two Be: A New Companion detection for HD 52244 using HST/FGS

Abstract

In this paper we present a newly detected companion to the Be star, HD 52244 (B2IVnpe), using the Fine Guidance Sensors (FGSs) on the Hubble Space Telescope (HST). In fall 2021, HST became momentarily unavailable to support nominal operations, and we used the operational FGS to carry out a multiplicity survey of 6 Be stars. We were able to resolve a companion to HD 52244, with a separation of 42.7 +/- 1.1 mas (74 AU) and a position angle of 144.2 +/- 0.3 with a differential magnitude in the F583W filter of 1.91 +/- 0.02 mag. This study presents the results to the newly detected companion of HD 52244 and lays the groundwork for future studies looking for wide or third companions to Be stars.

Figures (9)

• Figure 1: Presented here are the spectra of the six Be stars in this study. To the left is the visible light spectrum (with the exception of HD 206135 where it is IR from APOGEE ;Apogee) of the 6 of Be from the BeSS Database Neiner2018 and the right postage stamp size plots are around the H$\alpha$ emission from the low resolution spectra from GaiaDR3.
• Figure 2: Comparison of rectified (solid) and not rectified (dashed) $S$-curve of calibrator HD 50737. The $x$-axis is the instantaneous field of view of the FGS where 0 is the center of light.
• Figure 3: The $x$ (right) and $y$ (left) $S$-curves from the STSci least squares fitting for HD 52244. For both plots the red line is the observed $S$=curve and the blue dotted line is the model. The black line at the bottom is the difference between the two.
• Figure 4: This plot shows the model fit from the CCF and second derivative test for HD 52244 in $x$ (left) and $y$ (right). The top row is the mean residuals from the cross correlation routine. The solid black line is the CCF result after removing the primary component. The gray line is the calculated standard deviation and the vertical dashed line indicates where a component was detected (one in $x$, two in $y$). The middle row is the fit (dashed line) and the observed (solid line) from the CCF. The bottom row shows the results from the second derivative test. The solid black line is the observed minus model residuals and the gray region is the standard deviation of the ensemble of calibrator $S$-curves. The red line, present only on the $x$-axis plots, is the second derivative of the $S$-curve, indicating that while the system is not resolved in $x$ with the CCF, it deviates from a point source in $x$ with the second derivative test.
• Figure 5: This plot shows the model fit from the CCF and second derivative test for HD 239618 in $x$ (left) and $y$ (right). The top row is the mean residuals from the cross correlation routine. The solid black line is the CCF result after removing the primary component. The gray line is the calculated standard deviation and the vertical dashed line indicates where a component was detected. The middle row is the fit (dashed line) and the observed (solid line) from the CCF. The bottom row shows the results from the second derivative test. The solid black line is the observed minus model residuals and the gray region is the standard deviation of the ensemble of calibrator $S$-curves.