TY  - JOUR
A1  - Ghosh, H.
A1  - DePoy, D. L.
A1  - Gal-Yam, A.
A1  - Gaudi, B. S.
A1  - Gould, A.
A1  - Han, C.
A1  - Lipkin, Y.
A1  - Maoz, D.
A1  - Ofek, E. O.
A1  - Park, B. G.
A1  - Pogge, R. W.
A1  - Salim, S.
A1  - Abe, Fumio
A1  - Bennett, David P.
A1  - Bond, I. A.
A1  - Eguchi, S.
A1  - Furuta, Y.
A1  - Hearnshaw, John B.
A1  - Kamiya, K.
A1  - Kilmartin, Pam M.
A1  - Kurata, Y.
A1  - Masuda, Kimiaki
A1  - Matsubara, Yutaka
A1  - Muraki, Y.
A1  - Noda, S.
A1  - Okajima, K.
A1  - Rattenbury, N. J.
A1  - Sako, T.
A1  - Sekiguchi, T.
A1  - Sullivan, D. J.
A1  - Sumi, T.
A1  - Tristram, P. J.
A1  - Yanagisawa, T.
A1  - Yock, P. C. M.
A1  - Udalski, A.
A1  - Soszynski, I.
A1  - Wyrzykowski, X.
A1  - Kubiak, Marcin
A1  - Szymanski, M. K.
A1  - Pietrzynski, G.
A1  - Szewczyk, O.
A1  - Zebru, 
T1  - Potential direct single-star mass measurement
N2  - We analyze the light curve of the microlensing event OGLE-2003-BLG-175/MOA-2003-BLG-45 and show that it has two properties that, when combined with future high-resolution astrometry, could lead to a direct, accurate measurement of the lens mass. First, the light curve shows clear signs of distortion due to the Earth's accelerated motion, which yields a measurement of the projected Einstein radius (r) over tilde (E). Second, from precise astrometric measurements, we show that the blended light in the event is coincident with the microlensed source to within about 15 mas. This argues strongly that this blended light is the lens and hence opens the possibility of directly measuring the lens- source relative proper motion mu(rel) and so the mass M=(c(2)/4G)mu(rel)t(E)(r) over tilde (E), where t(E) is the measured Einstein timescale. While the light-curve-based measurement of (r) over tildeE is, by itself, severely degenerate, we show that this degeneracy can be completely resolved by measuring the direction of proper motion mu(rel)
Y1  - 2004
SN  - 0004-637X
ER  - 
TY  - JOUR
A1  - Jiang, G. F.
A1  - DePoy, D. L.
A1  - Gal-Yam, A.
A1  - Gaudi, B. S.
A1  - Gould, A.
A1  - Han, C.
A1  - Lipkin, Y.
A1  - Maoz, D.
A1  - Ofek, E. O.
A1  - Park, B. G.
A1  - Pogge, R. W.
A1  - Udalski, A.
A1  - Kubiak, Marcin
A1  - Szymanski, M. K.
A1  - Szewczyk, O.
A1  - Zerbrun, K.
A1  - Wyrzykowski, L.
A1  - Soszynski, I.
A1  - Pietrzynski, G.
A1  - Albrow, Michael D.
A1  - Beaulieu, Jean-Philippe
A1  - Caldwell, John A. R.
A1  - Cassan, A.
A1  - Coutures, C.
A1  - Dominik, M.
A1  - Donatowicz, J.
A1  - Fouque, P.
A1  - Greenhill, John
A1  - Hill, K.
A1  - Horne, Keith
A1  - Jorgensen, S. F.
A1  - Jorgensen, Uffe Grae
A1  - Kane, Stephen R.
A1  - Kubas, Daniel
A1  - Martin, Ralph
A1  - Menzies, J. W.
A1  - Pollard, R.
A1  - Sahu, K. C.
A1  - Wambsganss, Joachim
A1  - Watson, R.
A1  - Williams, A.
T1  - OGLE-2003-BLG-238 : Microlensing mass estimate of an isolated star
N2  - Microlensing is the only known direct method to measure the masses of stars that lack visible companions. In terms of microlensing observables, the mass is given by M (c(2)/4G)(r) over tilde (E)theta(E) and so requires the measurement of both the angular Einstein radius theta(E) and the projected Einstein radius (r) over tilde (E). Simultaneous measurement of these two parameters is extremely rare. Here we analyze OGLE-2003-BLG-238, a spectacularly bright (I-min 10.3), high-magnification (A(max) 170) microlensing event. Pronounced finite-source effects permit a measurement of theta(E) = 650 muas. Although the timescale of the event is only t(E) 38 days, one can still obtain weak constraints on the microlens parallax: 4.4 AU < <(r)over tilde>(E) < 18 AU at the 1 &sigma; level. Together these two parameter measurements yield a range for the lens mass of 0.36 M-&ODOT; < M < 1.48 M-&ODOT;. As was the case for MACHO- LMC-5, the only other single star (apart from the Sun) whose mass has been determined from its gravitational effects, this estimate is rather crude. It does, however, demonstrate the viability of the technique. We also discuss future prospects for single-lens mass measurements
Y1  - 2004
SN  - 0004-637X
ER  - 
TY  - JOUR
A1  - Charpinet, Stéphane
A1  - Brassard, P.
A1  - Fontaine, G.
A1  - Van Grootel, Valerie
A1  - Zong, Weika
A1  - Giammichele, N.
A1  - Heber, Ulrich
A1  - Bognár, Zsófia
A1  - Geier, Stephan
A1  - Green, Elizabeth M.
A1  - Hermes, J. J.
A1  - Kilkenny, D.
A1  - Ostensen, R. H.
A1  - Pelisoli, Ingrid Domingos
A1  - Silvotti, R.
A1  - Telting, J. H.
A1  - Vuckovic, Maja
A1  - Worters, H. L.
A1  - Baran, Andrzej S.
A1  - Bell, Keaton J.
A1  - Bradley, Paul A.
A1  - Debes, J. H.
A1  - Kawaler, S. D.
A1  - Kolaczek-Szymanski, P.
A1  - Murphy, S. J.
A1  - Pigulski, A.
A1  - Sodor, A.
A1  - Uzundag, Murat
A1  - Handberg, R.
A1  - Kjeldsen, H.
A1  - Ricker, G. R.
A1  - Vanderspek, R. K.
T1  - TESS first look at evolved compact pulsators Discovery and asteroseismic probing of the g-mode hot B subdwarf pulsator EC 21494-7018
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. The TESS satellite was launched in 2018 to perform high-precision photometry from space over almost the whole sky in a search for exoplanets orbiting bright stars. This instrument has opened new opportunities to study variable hot subdwarfs, white dwarfs, and related compact objects. Targets of interest include white dwarf and hot subdwarf pulsators, both carrying high potential for asteroseismology. Aims. We present the discovery and detailed asteroseismic analysis of a new g-mode hot B subdwarf (sdB) pulsator, EC 21494-7018 (TIC 278659026), monitored in TESS first sector using 120-s cadence. Methods. The TESS light curve was analyzed with standard prewhitening techniques, followed by forward modeling using our latest generation of sdB models developed for asteroseismic investigations. By simultaneously best-matching all the observed frequencies with those computed from models, we identified the pulsation modes detected and, more importantly, we determined the global parameters and structural configuration of the star. Results. The light curve analysis reveals that EC 21494-7018 is a sdB pulsator counting up to 20 frequencies associated with independent g-modes. The seismic analysis singles out an optimal model solution in full agreement with independent measurements provided by spectroscopy (atmospheric parameters derived from model atmospheres) and astrometry (distance evaluated from Gaia DR2 trigonometric parallax). Several key parameters of the star are derived. Its mass (0.391 +/- 0.009x2006;M-circle dot) is significantly lower than the typical mass of sdB stars and suggests that its progenitor has not undergone the He-core flash; therefore this progenitor could originate from a massive (greater than or similar to 2;M-circle dot) red giant, which is an alternative channel for the formation of sdBs. Other derived parameters include the H-rich envelope mass (0.0037 +/- 0.0010;M-circle dot), radius (0.1694 +/- 0.0081;R-circle dot), and luminosity (8.2 +/- 1.1;L-circle dot). The optimal model fit has a double-layered He+H composition profile, which we interpret as an incomplete but ongoing process of gravitational settling of helium at the bottom of a thick H-rich envelope. Moreover, the derived properties of the core indicate that EC 21494-7018 has burnt similar to 43% (in mass) of its central helium and possesses a relatively large mixed core (M-core;=;0.198 +/- 0.010;M-circle dot), in line with trends already uncovered from other g-mode sdB pulsators analyzed with asteroseismology. Finally, we obtain for the first time an estimate of the amount of oxygen (in mass; X(O)(core) = 0.16(-0.05)(+0.13)X(O)core=0.16-0.05+0.13$ X(mathrm{O})_{mathrm{core}}=0.16_{-0.05}<^>{+0.13} $) produced at this stage of evolution by an helium-burning core. This result, along with the core-size estimate, is an interesting constraint that may help to narrow down the still uncertain C-12(alpha,;gamma)O-16 nuclear reaction rate.
KW  - asteroseismology
KW  - stars
KW  - interiors
KW  - oscillations
KW  - horizontal-branch
KW  - individual
KW  - TIC 278659026
KW  - subdwarfs
Y1  - 2019
U6  - https://doi.org/10.1051/0004-6361/201935395
SN  - 0004-6361
SN  - 1432-0746
VL  - 632
PB  - EDP Sciences
CY  - Les Ulis
ER  -