A spectroscopic follow-up for Gaia19bld^★

¹ Las Cumbres Observatory, 6740 Cortona Drive, Suite 102, 93117 Goleta, CA, USA
e-mail: etibachelet@gmail.com
² Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
³ Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut, Mönchhofstr. 12-14, 69120 Heidelberg, Germany
⁴ Institut d’Astrophysique de Paris, Sorbonne Université, CNRS, UMR 7095, 98 bis bd Arago, 75014 Paris, France
⁵ Department of Physics, University of California, Santa Barbara, CA 93106-9530, USA

Received: 28 September 2020
Accepted: 1 July 2021

Abstract

Context. Due to their scarcity, microlensing events in the Galactic disk are of great interest and high-cadence photometric observations, supplemented by spectroscopic follow-up, are necessary for constraining the physical parameters of the lensing system. In particular, a precise estimate of the source characteristics is required to accurately measure the lens distance and mass.

Aims. We conducted a spectroscopic follow-up of microlensing event Gaia19bld to derive the properties of the microlensing source and, ultimately, to estimate the mass and distance of the lens.

Methods. We obtained low- and high-resolution spectroscopy from multiple sites around the world during the course of the event. The spectral lines and template matching analysis has led to two independent, consistent characterizations of the source.

Results. We found that the source is a red giant located at ~8.5 kpc from the Earth. Combining our results with the photometric analysis has led to a lens mass of M_l ~ 1.1 M_⊙ at a distance of D_l ~ 5.5 kpc. We did not find any significant blend light in the spectra (with an upper detection limit of V ≤ 17 mag), which is in agreement with photometric observations. Therefore, we cannot exclude the possibility that the lens is a main-sequence star. Indeed, we predict in this scenario a lens brightness of V ~ 20 mag, a value that would make it much fainter than the detection limit.