J/A+A/619/A50 Spiral potential of the Milky Way (Grosboel+, 2018)
The spiral potential of the Milky Way.
Grosboel P., Carraro G.
<Astron. Astrophys. 619, A50 (2018)>
=2018A&A...619A..50G 2018A&A...619A..50G (SIMBAD/NED BibCode)
ADC_Keywords: Stars, normal ; Radial velocities ; Extinction; Spectroscopy ;
Galactic plane
Keywords: Galaxy: disk - Galaxy: structure - Galaxy: kinematics and dynamics -
stars: early-type - techniques: spectroscopic
Abstract:
The location of young sources in the Galaxy suggests a four-armed
spiral structure, whereas tangential points of spiral arms observed in
the integrated light at infrared and radio wavelengths indicate that
only two arms are massive.
Variable extinction in the Galactic plane and high light-to-mass
ratios of young sources make it difficult to judge the total mass
associated with the arms outlined by such tracers. The current
objective is to estimate the mass associated with the Sagittarius arm
by means of the kinematics of the stars across it.
Spectra of 1726 candidate B- and A-type stars within 3° of the
Galactic center (GC) were obtained with the FLAMES instrument at the
VLT with a resolution of ∼6000 in the spectral range of 396-457nm.
Radial velocities were derived by least-squares fits of the spectra to
synthetic ones. The final sample was limited to 1507 stars with either
Gaia DR2 parallaxes or main-sequence B-type stars having reliable
spectroscopic distances.
The solar peculiar motion in the direction of the GC relative to the
local standard of rest (LSR) was estimated to U☉=10.7±1.3km/s.
The variation in the median radial velocity relative to the LSR as a
function of distance from the sun shows a gradual increase from
slightly negative values near the sun to almost 5km/s at a distance of
around 4kpc. A sinusoidal function with an amplitude of 3.4±1.3km/s
and a maximum at 4.0±0.6kpc inside the sun is the best fit to the
data. A positive median radial velocity relative to the LSR around
1.8kpc, the expected distance to the Sagittarius arm, can be excluded
at a 99% level of confidence. A marginal peak detected at this
distance may be associated with stellar streams in the star-forming
regions, but it is too narrow to be associated with a major arm
feature.
A comparison with test-particle simulations in a fixed galactic
potential with an imposed spiral pattern shows the best agreement with
a two-armed spiral potential having the Scutum-Crux arm as the next
major inner arm. A relative radial forcing dFr∼1.5% and a pattern
speed in the range of 20-30km/s/kpc yield the best fit. The
lack of a positive velocity perturbation in the region around the
Sagittarius arm excludes it from being a major arm. Thus, the main
spiral potential of the Galaxy is two-armed, while the Sagittarius arm
is an inter-arm feature with only a small mass perturbation associated
with it.
Description:
Catalog of barycentric radial velocities of 1505 stars with B<15mag
and within 3° of the Galactic center based on FLAMES/VLT spectra
in the wavelength range of 396-457nm with a spectral resolution of
6000. Sources with a signal-to-noise ratio lager than 10 are included.
A total of 1472 sources is in the VVV catalog while 1498 coincided
with sources in the Gaia DR2 database. Cross-correlation with
synthetic spectra allowed to estimate the effective temperature of the
stars whereas surface gravity could be computed only for sources with
log(Teff)>4.0. Extinctions in the Ks band were calculated from the
near-infrared colors and effective temperatures. Distances were
computed from the Gaia DR2 parallaxes supplemented with 45
spectroscopic distances for early-type, main-sequence stars. With
distances up to approx. 4kpc, the data reach beyond the Sagittarius
arm and were used to estimate the spiral potential of this arm. The
spectra are provided in relative intensities.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 202 1505 Catalog of radial velocities
catalog.fit 2880 6453 Catalog of radial velocities with spectra
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
II/348 : VISTA Variable in the Via Lactea Survey DR2 (Minniti+, 2017)
Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Ident Objective identifier
12- 17 A6 --- Field Field identifier
19- 21 I3 --- Fiber Fiber in field
23- 32 F10.6 deg RAdeg Right ascension (J2000)
34- 43 F10.6 deg DEdeg Declination (J2000)
45- 56 F12.6 d Obs.Date MJD of mean observation
58- 65 F8.4 --- SNR Signal-to-noise ratio
67- 85 I19 --- Gaia ? Gaia DR2 identifier
87- 94 F8.5 mag Gmag ? Gaia G magnitude
96-107 I12 --- VVV ? VVV identifier
109-115 F7.4 mag Kmag ? VVV Ks MAG1AP
117-127 F11.6 km/s BRV Barycentric radial velocity
129-137 F9.6 km/s e_BRV Radial velocity error
139-145 F7.5 [K] logTeff log10 of effective temperature
147-153 F7.5 [K] e_logTeff log10 of effective temperature error
155-161 F7.5 [cm/s2] logg ? log10 of surface gravity
163-171 F9.6 mag Ak ? Extinction in Ks
173-183 F11.6 kpc Dist ? Distance from sun
185-193 F9.6 kpc Dist-sp ? Spectroscopic distance from sun
195-197 I3 nm Start [396] Wavelength start of spectrum
199-202 F4.2 nm Step [0.02] Step size of spectrum
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Acknowledgements:
Preben Grosboel, pgrosbol(at)eso.org>
(End) Preben Grosboel [ESO], Patricia Vannier [CDS] 13-Sep-2018