scholarly journals Structure and kinematics of Type II Cepheids in the Galactic bulge based on near-infrared VVV data

2018 ◽  
Vol 619 ◽  
pp. A51 ◽  
Author(s):  
V. F. Braga ◽  
A. Bhardwaj ◽  
R. Contreras Ramos ◽  
D. Minniti ◽  
G. Bono ◽  
...  
Keyword(s):  
Proper Motion ◽  
Stellar Population ◽  
Near Infrared ◽  
Galactic Center ◽  
Tangential Velocity ◽  
Type Ii ◽  
Galactic Bulge ◽  
Rr Lyrae ◽  
Sgr A ◽  
Kinematic Properties

Context. Type II Cepheids (T2Cs) are radially pulsating variables that trace old stellar populations and provide distance estimates through their period-luminosity (PL) relation. Aims. We trace the structure of old stellar population in the Galactic bulge using new distance estimates and kinematic properties of T2Cs. Methods. We present new near-infrared photometry of T2Cs in the bulge from the VISTA Variables in the Vía Láctea survey (VVV). We provide the largest sample (894 stars) of T2Cs with JHKs observations that have accurate periods from the Optical Gravitational Lensing Experiment (OGLE) catalog. Our analysis makes use of the Ks-band time-series observations to estimate mean magnitudes and individual distances by means of the PL relation. To constrain the kinematic properties of our targets, we complement our analysis with proper motions based on both the VVV and Gaia Data Release 2. Results. We derive an empirical Ks-band PL relation that depends on Galactic longitude and latitude: Ks0 = (10.66 ± 0.02) − (2.21 ± 0.03)·(log P−1.2)−(0.020±0.003)·l+(0.050±0.008)·|b| mag; individual extinction corrections are based on a 3D reddening map. Our targets display a centrally concentrated distribution, with solid evidence of ellipsoidal symmetry – similar to the RR Lyræ ellipsoid – and a few halo outliers up to ≳100 kpc. We obtain a distance from the Galactic center of R0 = 8.46 ± 0.03(stat.) ± 0.11(syst.) kpc. We also find evidence that the bulge T2Cs belong to a kinematically hot population, as the tangential velocity components (συl∗ = 104.2 ± 3.0kms−1 and συb = 96.8 ± 5.5kms−1) agree within 1.2σ. Moreover, the difference between absolute and relative proper motion is in good agreement with the proper motion of Sgr A✻ from VLBA measures. Conclusions. We conclude that bulge T2Cs display an ellipsoidal spatial distribution and have kinematics similar to RR Lyræ stars, which are other tracers of the old, low-mass stellar population. T2Cs also provide an estimate of R0 that agrees excellently well with the literature, taking account of the reddening law.

scholarly journals New type II Cepheids from VVV data towards the Galactic center

2019 ◽  
Vol 625 ◽  
pp. A151 ◽  
Author(s):  
V. F. Braga ◽  
R. Contreras Ramos ◽  
D. Minniti ◽  
C. E. Ferreira Lopes ◽  
M. Catelan ◽  
...  
Keyword(s):  
Near Infrared ◽  
Galactic Center ◽  
Variable Stars ◽  
Type Ii ◽  
Statistical Parameters ◽  
Rr Lyrae ◽  
Classical Cepheids ◽  
Starting Point ◽  
The Galaxy ◽  
New Type

Context. The Galactic center (GC) is the densest region of the Milky Way. Variability surveys towards the GC potentially provide the largest number of variable stars per square degree within the Galaxy. However, high stellar density is also a drawback due to blending. Moreover, the GC is affected by extreme reddening, therefore near infrared observations are needed. Aims. We plan to detect new variable stars towards the GC, focusing on type II Cepheids (T2Cs) which have the advantage of being brighter than RR Lyrae stars. Methods. We perform parallel Lomb-Scargle and Generalized Lomb-Scargle periodogram analysis of the Ks-band time series of the VISTA variables in the Vía Láctea survey, to detect periodicities. We employ statistical parameters to clean our sample. We take account of periods, light amplitudes, distances, and proper motions to provide a classification of the candidate variables. Results. We detected 1019 periodic variable stars, of which 164 are T2Cs, 210 are Miras and 3 are classical Cepheids. We also found the first anomalous Cepheid in this region. We compare their photometric properties with overlapping catalogs and discuss their properties on the color-magnitude and Bailey diagrams. Conclusions. We present the most extensive catalog of T2Cs in the GC region to date. Offsets in E(J − Ks) and in the reddening law cause very large (∼1–2 kpc) uncertainties on distances in this region. We provide a catalog which will be the starting point for future spectroscopic surveys in the innermost regions of the Galaxy.

scholarly journals Stellar parameters in the bulge cluster NGC 6553

1997 ◽  
Vol 189 ◽  
pp. 203-206 ◽  
Author(s):  
B. Barbuy ◽  
S. Ortolani ◽  
E. Bica ◽  
A. Renzini ◽  
M.D. Guarnieri
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Spectroscopic Analysis ◽  
Galactic Center ◽  
Stellar Populations ◽  
The Sun ◽  
Galactic Bulge ◽  
Complete Understanding ◽  
Luminosity Functions ◽  
Bulge Formation

Globular clusters in the Galactic bulge form a flattened system, extending from the Galactic center to about 4.5 kpc from the Sun (Barbuy et al. 1997). A study of abundance ratios in these clusters is very important for a more complete understanding of the bulge formation. In this work we present a spectroscopic analysis of individual stars in NGC 6553. This cluster is a key one because it is located at d⊙ ≍ 5.1 kpc, therefore relatively close to us, and at the same time it is representative of the Galactic bulge stellar population: (a) Ortolani et al. (1995) showed that NGC 6553 and NGC 6528 show very similar Colour-Magnitude Diagrams (CMDs), and NGC 6528 is located at d⊙ ≍ 7.83 kpc, very close to the Galactic center; (b) the stellar populations of the Baade Window is also very similar to that of NGC 6553 and NGC 6528 as Ortolani et al. (1995) have shown by comparing their luminosity functions.

scholarly journals Search for variable stars in globular clusters

1986 ◽  
Vol 118 ◽  
pp. 287-288
Author(s):  
M. L. Hazen-Liller
Keyword(s):  
Globular Clusters ◽  
Galactic Center ◽  
Variable Stars ◽  
Galactic Bulge ◽  
Rr Lyrae ◽  
High Metallicity

A program to search poorly studied southern globular clusters for variable stars is being carried out on the 1-m Yale telescope at CTIO. Recently two galactic bulge clusters of moderately high metallicity have been found to contain RR Lyrae variables; a cluster of similar metallicity a little farther from the galactic center apparently has none.

scholarly journals BlackHoleCam: Fundamental physics of the galactic center

2017 ◽  
Vol 26 (02) ◽  
pp. 1730001 ◽  
Author(s):  
C. Goddi ◽  
H. Falcke ◽  
M. Kramer ◽  
L. Rezzolla ◽  
C. Brinkerink ◽  
...  
Keyword(s):  
Event Horizon ◽  
Near Infrared ◽  
Galactic Center ◽  
Strong Field ◽  
Current Knowledge ◽  
Current Status ◽  
Electromagnetic Spectrum ◽  
Fundamental Physics ◽  
Gravitational Fields ◽  
Sgr A

Einstein’s General theory of relativity (GR) successfully describes gravity. Although GR has been accurately tested in weak gravitational fields, it remains largely untested in the general strong field cases. One of the most fundamental predictions of GR is the existence of black holes (BHs). After the recent direct detection of gravitational waves by LIGO, there is now near conclusive evidence for the existence of stellar-mass BHs. In spite of this exciting discovery, there is not yet direct evidence of the existence of BHs using astronomical observations in the electromagnetic spectrum. Are BHs observable astrophysical objects? Does GR hold in its most extreme limit or are alternatives needed? The prime target to address these fundamental questions is in the center of our own Milky Way, which hosts the closest and best-constrained supermassive BH candidate in the universe, Sagittarius A* (Sgr A*). Three different types of experiments hold the promise to test GR in a strong-field regime using observations of Sgr A* with new-generation instruments. The first experiment consists of making a standard astronomical image of the synchrotron emission from the relativistic plasma accreting onto Sgr A*. This emission forms a “shadow” around the event horizon cast against the background, whose predicted size ([Formula: see text]as) can now be resolved by upcoming very long baseline radio interferometry experiments at mm-waves such as the event horizon telescope (EHT). The second experiment aims to monitor stars orbiting Sgr A* with the next-generation near-infrared (NIR) interferometer GRAVITY at the very large telescope (VLT). The third experiment aims to detect and study a radio pulsar in tight orbit about Sgr A* using radio telescopes (including the Atacama large millimeter array or ALMA). The BlackHoleCam project exploits the synergy between these three different techniques and contributes directly to them at different levels. These efforts will eventually enable us to measure fundamental BH parameters (mass, spin, and quadrupole moment) with sufficiently high precision to provide fundamental tests of GR (e.g. testing the no-hair theorem) and probe the spacetime around a BH in any metric theory of gravity. Here, we review our current knowledge of the physical properties of Sgr A* as well as the current status of such experimental efforts towards imaging the event horizon, measuring stellar orbits, and timing pulsars around Sgr A*. We conclude that the Galactic center provides a unique fundamental-physics laboratory for experimental tests of BH accretion and theories of gravity in their most extreme limits.

scholarly journals Detailed near-IR stellar abundances of red giants in the Inner Bulge and Galactic Center

2017 ◽  
Vol 13 (S334) ◽  
pp. 82-85
Author(s):  
N. Ryde ◽  
R. M. Rich ◽  
B. Thorsbro ◽  
M. Schultheis ◽  
T. K. Fritz ◽  
...  
Keyword(s):  
Stellar Population ◽  
Galactic Center ◽  
Galactic Plane ◽  
Star Cluster ◽  
High Dispersion ◽  
Red Giants ◽  
Galactic Bulge ◽  
Stellar Abundances ◽  
Near Ir ◽  
K Band

AbstractOwing to their extreme crowding and high and variable extinction, stars in the Galactic Bulge, within ±2° of the Galactic plane, and especially those in the Nuclear Star Cluster, have only rarely been targeted for an analyses of their detailed abundances. There is also some disagreement about the high end of the abundance scale for these stars. It is now possible to obtain high dispersion, high S/N spectra in the infrared K band (~2.0 − 2.4 µm) for these giants; we report our progress at Keck and VLT in using these spectra to infer the composition of this stellar population.

scholarly journals Detection of polarized continuum emission of the Dusty S-cluster Object (DSO/G2)

2016 ◽  
Vol 11 (S322) ◽  
pp. 233-234
Author(s):  
B. Shahzamanian ◽  
M. Zajaček ◽  
M. Valencia-S. ◽  
F. Peissker ◽  
A. Eckart ◽  
...  
Keyword(s):  
Near Infrared ◽  
Galactic Center ◽  
Continuum Emission ◽  
Polarization Angle ◽  
Imaging Data ◽  
Intrinsic Geometry ◽  
Infrared Excess ◽  
Geometrical Properties ◽  
Sgr A ◽  
First Time

AbstractA peculiar source in the Galactic center known as the Dusty S-cluster Object (DSO/G2) moves on a highly eccentric orbit around the supermassive black hole with the pericenter passage in the spring of 2014. Its nature has been uncertain mainly because of the lack of any information about its intrinsic geometry. For the first time, we use near-infrared polarimetric imaging data to obtain constraints about the geometrical properties of the DSO. We find out that DSO is an intrinsically polarized source, based on the significance analysis of polarization parameters, with the degree of the polarization of ~30% and an alternating polarization angle as it approaches the position of Sgr A*. Since the DSO exhibits a near-infrared excess of Ks-L′ > 3 and remains rather compact in emission-line maps, its main characteristics may be explained with the model of a pre-main-sequence star embedded in a non-spherical dusty envelope.

scholarly journals Near- and Mid-infrared Observations in the Inner Tenth of a Parsec of the Galactic Center Detection of Proper Motion of a Filament Very Close to Sgr A*

2020 ◽  
Vol 897 (1) ◽  
pp. 28 ◽  
Author(s):  
Florian Peißker ◽  
Andreas Eckart ◽  
Nadeen B. Sabha ◽  
Michal Zajaček ◽  
Harshitha Bhat
Keyword(s):  
Proper Motion ◽  
Galactic Center ◽  
Mid Infrared ◽  
Infrared Observations ◽  
Sgr A

scholarly journals 3.1. Long-term star formation at the Galactic center and its effect on the stellar population

1998 ◽  
Vol 184 ◽  
pp. 89-90
Author(s):  
E. Serabyn
Keyword(s):  
Star Formation ◽  
Stellar Population ◽  
Near Infrared ◽  
Galactic Center ◽  
Reference List ◽  
Complete Discussion ◽  
Nuclear Cluster ◽  
Lines Of Evidence

Star formation presently occurs in our Galactic nucleus at a rate of several 10−1 M⊙ yr−1. If this value represents the long-term average, some 109 M⊙ of stars should have been generated in our Galaxy's central few hundred parsec volume over the Milky Way's lifetime. As the expected stellar yield is actually in rough agreement with the mass of our Galaxy's bright near-infrared “central r−2 cluster”, it is possible to hypothesize that this massive “nuclear” cluster is in fact the product of long-term nuclear star-formation, rather than being a remnant of the Galaxy's formation epoch. Several lines of evidence supporting this hypothesis are laid out in Serabyn and Morris (1996), to which the reader is referred for a complete discussion and reference list; here only a brief summary of the main arguments is presented.

scholarly journals Unusually Wide, High-Velocity Radio Recombination Lines from G0.15–0.05 in the Radio Arc

1989 ◽  
Vol 136 ◽  
pp. 275-280 ◽  
Author(s):  
F. Yusef-Zadeh ◽  
Mark Morris ◽  
J. H. van Gorkom
Keyword(s):  
Radial Velocity ◽  
Galactic Center ◽  
Galactic Plane ◽  
Line Profiles ◽  
Recombination Line ◽  
Ionized Gas ◽  
Hii Region ◽  
Sgr A ◽  
Relativistic Particles ◽  
Kinematic Properties

The H92αrecombination line was observed at 8 GHz toward the “pistol-shaped” HII region G0.15–0.05 using the VLA2in its most compact configuration. The line profiles of individual components of this source peak at VLSR=123 km/s and have total line widths of ~90 km/s. The kinematical structure of the “pistol” is unusual in that much of the neutral and ionized gas in this region is seen predominantly at either +50 or +20 km/s. The line width and radial velocity are the largest found in the Galactic center region with the exception of Sgr A West. We also found gas at VLSR=140 km/s associated with G0.18–0.04: the sickle-shaped feature which surrounds G0.15–0.05. The kinematic properties of G0.18–0.04 and G0.15–0.05 suggest that these two features are components of a single, but complex thermal system interacting with the nonthermal filaments of the radio Arc. In this regard, the width of the broad recombination line from G0.15–0.05, and its large radial velocity, might be explained as the interaction of streaming relativistic particles in the nonthermal filaments of the Arc impacting upon ambient gas clouds lying in the Galactic plane.

scholarly journals A geometric distance measurement to the Galactic center black hole with 0.3% uncertainty

2019 ◽  
Vol 625 ◽  
pp. L10 ◽  
Author(s):  
◽  
R. Abuter ◽  
A. Amorim ◽  
M. Bauböck ◽  
J. P. Berger ◽  
...  
Keyword(s):  
Black Hole ◽  
Near Infrared ◽  
Galactic Center ◽  
Accurate Determination ◽  
Massive Black Hole ◽  
Geometric Distance ◽  
Significance Level ◽  
Beam Combiner ◽  
Infrared Interferometry ◽  
Sgr A

We present a 0.16% precise and 0.27% accurate determination of R0, the distance to the Galactic center. Our measurement uses the star S2 on its 16-year orbit around the massive black hole Sgr A* that we followed astrometrically and spectroscopically for 27 years. Since 2017, we added near-infrared interferometry with the VLTI beam combiner GRAVITY, yielding a direct measurement of the separation vector between S2 and Sgr A* with an accuracy as good as 20 μas in the best cases. S2 passed the pericenter of its highly eccentric orbit in May 2018, and we followed the passage with dense sampling throughout the year. Together with our spectroscopy, in the best cases with an error of 7 km s−1, this yields a geometric distance estimate of R0 = 8178 ± 13stat. ± 22sys. pc. This work updates our previous publication, in which we reported the first detection of the gravitational redshift in the S2 data. The redshift term is now detected with a significance level of 20σ with fredshift = 1.04 ± 0.05.

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