40 research outputs found
A Holistic Review of a Galactic Interaction
Our situation as occupants of the Milky Way (MW) Galaxy, bombarded by the
Sagittarius dwarf galaxy, provides an intimate view of physical processes that
can lead to the dynamical heating of a galactic disc. While this evolution is
instigated by Sagittarius, it is also driven by the intertwined influences of
the dark matter halo and the disc itself. We analyse an N-body simulation
following a Sagittarius-like galaxy interacting with a MW-like host to
disentangle these different influences during the stages of a minor merger. The
accelerations in the disc plane from each component are calculated for each
snapshot in the simulation, and then decomposed into Fourier series on annuli.
The analysis maps quantify and compare the scales of the individual
contributions over space and through time: (i) accelerations due to the
satellite are only important around disc passages; (ii) the influence around
these passages is enhanced and extended by the distortion of the dark matter
halo; (iii) the interaction drives disc asymmetries within and perpendicular to
the plane and the self-gravity of these distortions increase in importance with
time eventually leading to the formation of a bar. These results have
interesting implications for identifying different influences within our own
Galaxy. Currently, Sagittarius is close enough to a plane crossing to search
for localized signatures of its effect at intermediate radii, the distortion of
the MW's dark matter halo should leave its imprint in the outer disc and the
disc's own self-consistent response is sculpting the intermediate and inner
disc.Comment: 19 pages, 18 figures, published in the Monthly Notices of the Royal
Astronomical Societ
A celestial matryoshka: Dynamical and spectroscopic analysis of the Albireo system
We present a spectroscopic characterisation and a new orbital solution for
the binary system beta Cyg Aa/Ac (MCA 55), the primary component (beta Cyg A)
of the well-known wide double star Albireo. By matching evolutionary tracks to
the physical parameters of all three Albireo stars (beta Cyg Aa, Ac and B) as
obtained from a spectroscopic analysis of TIGRE and IUE spectra, we confirm
that they are likely coeval. Our final orbit solution is based on
radial-velocity measurements taken over a baseline exceeding years,
combined with relative astrometry from speckle interferometric observations and
the absolute astrometry from the Hipparcos and Gaia missions. Our final orbit
solution has a period of years with an eccentricity of
. Thanks to the inclusion of the absolute astrometry, we
find a mass ratio of , and a total mass of
M, indicating that the secondary (Ac) is the
more massive of the pair. These results strongly suggest the presence of a
fourth, unseen, member of the Albireo system. Given the current photometric
data it is likely that beta Cyg A is itself a hierarchical triple. We also
derive the systemic proper motion, line-of-sight velocity, and an orbital
parallax of the beta Cyg A system, allowing us to quantitatively assess the
hypothesis that Albireo A and B form a physically bound and genealogically
connected system. Finally, we find four potential members of a common proper
motion group with Albireo, though none anywhere as close by as the Albireo
components A to B.Comment: final draft of accepted manuscrip
Evidence of a vertical kinematic oscillation beyond the Radcliffe Wave
The Radcliffe Wave (RW) is a recently discovered sinusoidal vertical feature
of dense gas in the proximity of the Sun. In the disk plane, it is aligned with
the Local Arm. However, the origin of its vertical undulation is still unknown.
This study constrains the kinematics of the RW, using young stars and open
clusters as tracers, and explores the possibility of this oscillation being
part of a more extended vertical mode. We study the median vertical velocity
trends of the young stars and clusters along with the RW and extend it further
to the region beyond it. We discover a kinematic wave in the Galaxy, distinct
from the warp, with the amplitude of oscillation depending on the age of the
stellar population. We perform a similar analysis in the N-body simulation of a
satellite as massive as the Sagittarius dwarf galaxy impacting the galactic
disk. When projected in the plane, the spiral density wave induced by the
satellite impact is aligned with the RW, suggesting that both may be the
response of the disk to an external perturbation. However, the observed
kinematic wave is misaligned. It appears as a kinematic wave travelling
radially, winding up faster than the density wave matched by the RW,
questioning its origin. If a satellite galaxy is responsible for this kinematic
wave, we predict the existence of a vertical velocity dipole that should form
across the disk and this may be measurable with the upcoming Gaia DR3 and DR4.Comment: Accepted for publication in Astronomy & Astrophysics Letter
The Second-Generation Guide Star Catalog: Description and Properties
The GSC-II is an all-sky database of objects derived from the uncompressed
DSS that the STScI has created from the Palomar and UK Schmidt survey plates
and made available to the community. Like its predecessor (GSC-I), the GSC-II
was primarily created to provide guide star information and observation
planning support for HST. This version, however, is already employed at some of
the ground-based new-technology telescopes such as GEMINI, VLT, and TNG, and
will also be used to provide support for the JWST and Gaia space missions as
well as LAMOST, one of the major ongoing scientific projects in China. Two
catalogs have already been extracted from the GSC-II database and released to
the astronomical community. A magnitude-limited (R=18.0) version, GSC2.2, was
distributed soon after its production in 2001, while the GSC2.3 release has
been available for general access since 2007.
The GSC2.3 catalog described in this paper contains astrometry, photometry,
and classification for 945,592,683 objects down to the magnitude limit of the
plates. Positions are tied to the ICRS; for stellar sources, the all-sky
average absolute error per coordinate ranges from 0.2" to 0.28" depending on
magnitude. When dealing with extended objects, astrometric errors are 20% worse
in the case of galaxies and approximately a factor of 2 worse for blended
images. Stellar photometry is determined to 0.13-0.22 mag as a function of
magnitude and photographic passbands (B,R,I). Outside of the galactic plane,
stellar classification is reliable to at least 90% confidence for magnitudes
brighter than R=19.5, and the catalog is complete to R=20.Comment: 52 pages, 33 figures, to be published in AJ August 200
The Radcliffe Wave as the gas spine of the Orion Arm
The Radcliffe Wave is a kpc long coherent gas structure containing
most of the star-forming complexes near the Sun. In this Letter we aim to find
a Galactic context for the Radcliffe Wave by looking into a possible
relationship between the gas structure and the Orion (Local) Arm. We use
catalogs of massive stars and young open clusters based on \textit{Gaia} EDR3
astrometry, in conjunction with kiloparsec-scale 3D dust maps, to investigate
the Galactic \textit{XY} spatial distributions of gas and young stars. We find
a quasi-parallel offset between the luminous blue stars and the Radcliffe Wave,
in that massive stars and clusters are found essentially inside and downstream
from the Radcliffe Wave. We examine this offset in the context of color
gradients observed in the spiral arms of external galaxies, where the interplay
between density wave theory, spiral shocks, and triggered star formation has
been used to interpret this particular arrangement of gas/dust and OB stars,
and outline other potential explanations as well. We hypothesize that the
Radcliffe Wave constitutes the gas reservoir of the Orion (Local) Arm, and
presents itself as a prime laboratory to study the interface between Galactic
structure, the formation of molecular clouds in the Milky Way, and star
formation.Comment: Published in A&A Letter
The Construction of a Reference Star Catalog for the Euclid Mission
Optimization of scientific throughput from the ESA Euclid mission imposes stringent requirements on the performance of satellite absolute pointing. This will be achieved by the on-board Fine Guidance Sensor (FGS) with the aid of a specific stellar catalog, which must comply with well-defined, FGS-driven astrometric and photometric properties. By means of the OATo Star Catalog Database, used for the production of the Initial Gaia Source List, we present a preliminary assessment of the methods of construction of such a reference catalog