SPLUSJ210428.01-004934.2: An Ultra Metal-Poor Star Identified from
  Narrowband Photometry
  We report on the discovery of SPLUS J210428.01-004934.2, an ultra metal-poor
(UMP) star first identified from the narrow-band photometry of the Southern
Photometric Local Universe Survey (S-PLUS) Data Release 1, in the SDSS Stripe
82 region. Follow-up medium- and high-resolution spectroscopy (with Gemini
South and Magellan-Clay, respectively) confirmed the effectiveness of the
search for low-metallicity stars using the S-PLUS narrow-band photometry. At
[Fe/H]=-4.03, SPLUS J2104-0049 has the lowest detected carbon abundance,
A(C)=+4.34, when compared to the 34 previously known UMP stars in the
literature, which is an important constraint on its stellar progenitor and also
on stellar evolution models at the lowest metallicities. Based on its chemical
abundance pattern, we speculate that SPLUS J2104-0049 could be a bonafide
second-generation star, formed from a gas cloud polluted by a single metal-free
~30Mo star. This discovery opens the possibility of finding additional UMP
stars directly from narrow-band photometric surveys, a potentially powerful
method to help complete the inventory of such peculiar objects in our Galaxy.
