A J-band detection of the sub-stellar mass donor in SDSS J1433+1011

TL;DR

This study reports the first spectroscopic detection of a sub-stellar donor in a cataclysmic variable, identifying its spectral type and radial velocity, thus providing new insights into such systems' evolution.

Contribution

It presents the first spectroscopic detection and spectral classification of a sub-stellar donor in a cataclysmic variable, confirming evolutionary model predictions.

Findings

Detected sub-stellar donor contributing 38% to J-band light

Estimated donor spectral type as L2 +/- 1

Derived donor radial velocity as 520 +/- 60 km/s

Abstract

We present time-resolved J-band spectroscopy of the short period cataclysmic variable SDSS J143317.78+101123.3. We detect absorption lines from the sub-stellar donor star in this system, which contributes 38 +/- 5% to the J-band light. From the relative strengths of the absorption lines in the J-band, we estimate the spectral type of the donor star to be L2 +/- 1. These data are the first spectroscopic detection of a confirmed sub-stellar donor in a cataclysmic variable, and the spectral type is consistent with that expected from semi-empirical evolutionary models. Using skew mapping, we have been able to derive an estimate for the radial velocity of the donor of Kd = 520 +/- 60 km/s. This value is consistent with, though much less precise than, predictions from mass determinations found via photometric fitting of the eclipse light curves.