The Binary Dwarf Carbon Star SDSS J125017.90+252427.6

TL;DR

This paper reports the first detection of photometric and spectroscopic binarity in a dwarf carbon star, SDSS J125017.90+252427.6, providing direct evidence supporting the binary origin of dwarf carbon stars.

Contribution

It presents the first photometric binary detection in a dwarf carbon star and confirms binarity through radial velocity measurements, advancing understanding of their formation.

Findings

First photometric binary detection in a dwarf carbon star.

Radial velocity amplitude consistent with a white dwarf companion.

Photometric variations likely due to reflection effects from an unseen companion.

Abstract

Although dwarf carbon (dC) stars are thought universally to be binaries to explain the presence of $C_2$ in their spectra while still near main sequence luminosity, direct observational evidence for binarity is remarkably scarce. Here we report the detection of a 2.92 d periodicity in both photometry and radial velocity of SDSS J125017.90+252427.6, an $r=16.4$ dC star. This is the first photometric binary dC, and only the second dC spectroscopic binary. The relative phase of the photometric period to the spectroscopic observations suggests that the photometric variations are a reflection effect due to heating from an unseen companion. The observed radial velocity amplitude of the dC component ($K = 98.8\pm10.7$ km/s) is consistent with a white dwarf companion, presumably the evolved star that earlier donated the carbon to the dC, although substantial orbital evolution must have occurred. Large synoptic photometric surveys such as the Palomar Transient Factory, used for this work, may prove useful for identifying binaries among the shorter period dC stars.