17 research outputs found
Stellar-mass black holes in the Hyades star cluster?
Astrophysical models of binary-black hole mergers in the Universe require a
significant fraction of stellar-mass black holes (BHs) to receive negligible
natal kicks to explain the gravitational wave detections. This implies that BHs
should be retained even in open clusters with low escape velocities
(). We search for signatures of the presence
of BHs in the nearest open cluster to the Sun - the Hyades - by comparing
density profiles of direct -body models to data from . The
observations are best reproduced by models with BHs at present. Models
that never possessed BHs have an half-mass radius smaller than the
observed value, while those where the last BHs were ejected recently
(Myr ago) can still reproduce the density profile. In 50% of the
models hosting BHs, we find BHs with stellar companion(s). Their period
distribution peaks at yr, making them unlikely to be found through
velocity variations. We look for potential BH companions through large
astrometric and spectroscopic errors, identifying 56 binary candidates - none
of which consistent with a massive compact companion. Models with BHs
have an elevated central velocity dispersion, but observations can not yet
discriminate. We conclude that the present-day structure of the Hyades requires
a significant fraction of BHs to receive natal kicks smaller than the escape
velocity of at the time of BH formation and
that the nearest BHs to the Sun are in, or near, Hyades.Comment: 20 pages, 15 figures, 5 tables. Accepted for publication in MNRAS.
Comments welcom
Radial velocities from Gaia BP/RP spectra
The Gaia mission has provided us full astrometric solutions for over B
sources. However, only the brightest 34M of those have radial velocity
measurements. As a proof of concept, this paper aims to close that gap, by
obtaining radial velocity estimates from the low-resolution BP/RP spectra that
Gaia now provides. These spectra are currently published for about 220M
sources, with this number increasing to the full B Gaia sources with
Gaia Data Release 4. To obtain the radial velocity measurements, we fit Gaia
BP/RP spectra with models based on a grid of synthetic spectra, with which we
obtain the posterior probability on the radial velocity for each object. Our
measured velocities show systematic biases that depend mainly on colours and
magnitudes of stars. We correct for these effects by using external catalogues
of radial velocity measurements. We present in this work a catalogue of about
M sources with our most reliable radial velocity measurements and
uncertainties km s obtained from the BP/RP spectra. About 23% of
these have no previous radial velocity measurement in Gaia RVS. Furthermore, we
provide an extended catalogue containing all 125M sources for which we were
able to obtain radial velocity measurements. The latter catalogue, however,
also contains a fraction of measurements for which the reported radial
velocities and uncertainties are inaccurate. Although typical uncertainties in
the catalogue are significantly higher compared to those obtained with
precision spectroscopy instruments, the number of potential sources for which
this method can be applied is orders of magnitude higher than any previous
radial velocity catalogue. Further development of the analysis could therefore
prove extremely valuable in our understanding of Galactic dynamics.Comment: 14 pages, 17 figures, submitted to A&A, comments welcom
Astrobites as a Community-led Model for Education, Science Communication, and Accessibility in Astrophysics
Support for early career astronomers who are just beginning to explore
astronomy research is imperative to increase retention of diverse practitioners
in the field. Since 2010, Astrobites has played an instrumental role in
engaging members of the community -- particularly undergraduate and graduate
students -- in research. In this white paper, the Astrobites collaboration
outlines our multi-faceted online education platform that both eases the
transition into astronomy research and promotes inclusive professional
development opportunities. We additionally offer recommendations for how the
astronomy community can reduce barriers to entry to astronomy research in the
coming decade
Recommended from our members
The Astrometric Contribution of Unresolved Stellar Companions
No astronomical body is alone - some fraction of the mass of a system will always be found in orbiting bodies, ranging from fragmented debris to planets, stars and compact objects. In general we ‘see’ the brighter component: one star often dominates the detectable light, obscuring the companion - and we must turn to indirect methods to infer its presence.
Astrometry, the mapping of the motion of stars across the sky, is one such method. A significant mass concentrated in one or more collapsed companions will perturb the path. In the simplest and most ubiquitous case, a binary system, this perturbation is regular and easily described - a metronome beat added to the celestial motion. However, the combination of a star’s proper and parallactic motion with a binary orbit is non-linear, biasing our measurements of the system’s distance and motion and introducing extra astrometric noise.
In this thesis we will detail the astrometric impact of a binary companion, how it changes our inferences about systems assumed to be single bodies, and how we can detect companions through the deviations from single body fits. This is especially relevant to the current and ongoing Gaia survey, which is building astrometric tracks at unprecedented
(sub milli-arcsecond) precision and for the first time allowing us to detect a large number of unresolved but astrometrically significant binary systems. We present analytic expressions for the binary contribution, as well as an exploration of the behavior of simulated systems and detections of real binary candidates in the local galaxy