- ID:
- ivo://CDS.VizieR/J/A+A/614/A116
- Title:
- Masgomas-6 near-IR spectra
- Short Name:
- J/A+A/614/A116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent near-infrared data have contributed to unveiling massive and obscured stellar populations in both new and previously known clusters in our Galaxy. These discoveries have lead us to view the Milky Way as an active star-forming machine. We look for young massive cluster candidates as over-densities of OB-type stars. The first search, focused on the Galactic direction l=38, resulted in the detection of two objects with a remarkable population of OB-type star candidates. With a modified version of the friends-of-friends algorithm AUTOPOP and using 2MASS and UKIDSS-GPS near-infrared (J, H, and K) photometry for one of our cluster candidates (Masgomas-6) we selected 30 stars for multi-object and long-slit H and K band spectroscopy. With the spectral classification and the near-infrared photometric data, we derive individual distance, extinction, and radial velocity. Of the 30 spectroscopically observed stars, 20 are classified as massive stars, including OB-types (dwarfs, giants and supergiants), two red supergiants, two Wolf-Rayets (WR122-11 and the new WR122-16), and one transitional object (the LBV candidate IRAS 18576+0341). The individual distances and radial velocities do not agree with a single cluster, indicating that we are observing two populations of massive stars in the same line of sight: Masgomas-6a and Masgomas-6b. The first group of massive stars, located at 3.9kpc, contains both Wolf-Rayets and most of the OB-dwarfs; the second group, located at 9.6kpc, hosts the LBV candidate and an evolved population of supergiants. We are able to identify massive stars at two Galactic arms, but we cannot clearly identify whether these massive stars form clusters or associations.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/780/173
- Title:
- Masses of giant molecular clouds in Milky Way
- Short Name:
- J/ApJ/780/173
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mass fraction of dense gas within giant molecular clouds (GMCs) of the Milky Way is investigated using ^13^CO data from the Five College Radio Astronomy Observatory Galactic Plane Surveys and the Bolocam Galactic Plane Survey (BGPS) of 1.1mm dust continuum emission. A sample of 860 compact dust sources are selected from the BGPS catalog and kinematically linked to 344 clouds of extended (>3') ^13^CO J=1-0 emission. Gas masses are tabulated for the full dust source and subregions within the dust sources with mass surface densities greater than 200M_{sun}_/pc^2^, which are assumed to be regions of enhanced volume density. Masses of the parent GMCs are calculated assuming optically thin ^13^CO J=1-0 emission and local thermodynamic equilibrium conditions. The mean fractional mass of dust sources to host GMC mass is 0.11^+0.12^_-0.06__. The high column density subregions comprise 0.07^+0.13^_-0.05_ of the mass of the cloud. Owing to our assumptions, these values are upper limits to the true mass fractions. The fractional mass of dense gas is independent of GMC mass and gas surface density. The low dense gas mass fraction suggests that the formation of dense structures within GMCs is the primary bottleneck for star formation. The distribution of velocity differences between the dense gas and the low density material along the line of sight is also examined. We find a strong, centrally peaked distribution centered on zero velocity displacement. This distribution of velocity differences is modeled with radially converging flows toward the dense gas position that are randomly oriented with respect to the observed line of sight. These models constrain the infall velocities to be 2-4km/s for various flow configurations.
- ID:
- ivo://CDS.VizieR/J/ApJ/816/42
- Title:
- Mass models for the Milky Way
- Short Name:
- J/ApJ/816/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mass distribution of the Galactic disk is constructed from the terminal velocity curve and the mass discrepancy-acceleration relation. Mass models numerically quantifying the detailed surface density profiles are tabulated. For R_0_=8kpc, the models have stellar mass 5<M_*_<6x10^10^M_{sun}_, scale length 2.0<=R_d_<=2.9kpc, LSR circular velocity 222<={Theta}_0_<=233km/s, and solar circle stellar surface density 34<={Sigma}_d_(R_0_)<=61M_{sun}_/pc2. The present interarm location of the solar neighborhood may have a somewhat lower stellar surface density than average for the solar circle. The Milky Way appears to be a normal spiral galaxy that obeys scaling relations like the Tully-Fisher relation, the size-mass relation, and the disk maximality-surface brightness relation. The stellar disk is maximal, and the spiral arms are massive. The bumps and wiggles in the terminal velocity curve correspond to known spiral features (e.g., the Centaurus arm is a ~50% overdensity). The rotation curve switches between positive and negative over scales of hundreds of parsecs. The rms amplitude <|dV/dR|^2^>^1/2^, implying that commonly neglected terms in the Jeans equations may be nonnegligible. The spherically averaged local dark matter density is {rho}_0,DM_~0.009M_{sun}_/pc3 (0.34GeV/cm3). Adiabatic compression of the dark matter halo may help reconcile the Milky Way with the c-V_200_ relation expected in {Lambda}CDM while also helping to mitigate the too-big-to-fail problem, but it remains difficult to reconcile the inner bulge/bar-dominated region with a cuspy halo. We note that NGC 3521 is a near twin to the Milky Way, having a similar luminosity, scale length, and rotation curve.
- ID:
- ivo://CDS.VizieR/J/MNRAS/473/849
- Title:
- Mass segregation in Galactic stellar clusters
- Short Name:
- J/MNRAS/473/849
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We quantify the structure of a very large number of Galactic open clusters and look for evidence of mass segregation for the most massive stars in the clusters. We characterize the structure and mass segregation ratios of 1276 clusters in the Milky Way Stellar Cluster (MWSC) catalogue containing each at least 40 stars and that are located at a distance of up to ~2kpc from the Sun. We use an approach based on the calculation of the minimum spanning tree of the clusters, and for each one of them, we calculate the structure parameter Q and the mass segregation ratio {LAMBDA}_MSR_. Our findings indicate that most clusters possess a Q parameter that falls in the range 0.7-0.8 and are thus neither strongly concentrated nor do they show significant substructure. Only 27 per cent can be considered centrally concentrated with Q values >0.8. Of the 1276 clusters, only 14 per cent show indication of significant mass segregation ({LAMBDA}_MSR_>1.5). Furthermore, no correlation is found between the structure of the clusters or the degree of mass segregation with their position in the Galaxy. A comparison of the measured Q values for the young open clusters in the MWSC to N-body numerical simulations that follow the evolution of the Q parameter over the first 10Myr of the clusters life suggests that the young clusters found in the MWSC catalogue initially possessed local mean volume densities of {rho}*~=10-100M_{sun}_/pc^3^.
- ID:
- ivo://CDS.VizieR/J/A+A/571/A36
- Title:
- M dwarfs in b201 tile of VVV survey
- Short Name:
- J/A+A/571/A36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The intrinsically faint M dwarfs are the most numerous stars in the Galaxy, have main-sequence lifetimes longer than the Hubble time, and host some of the most interesting planetary systems known to date. Their identification and classification throughout the Galaxy is crucial to unraveling the processes involved in the formation of planets, stars, and the Milky Way. The ESO Public Survey VVV is a deep near-IR survey mapping the Galactic bulge and southern plane. The VVV b201 tile, located in the border area of the bulge, was specifically selected for the characterisation of M dwarfs. We used VISTA photometry to identify M dwarfs in the VVV b201 tile, to estimate their subtypes, and to search for transit-like light curves from the first 26 epochs of the survey.
- ID:
- ivo://CDS.VizieR/J/ApJ/885/3
- Title:
- Membership in 12 stellar streams from DES
- Short Name:
- J/ApJ/885/3
- Date:
- 16 Mar 2022 11:34:00
- Publisher:
- CDS
- Description:
- We cross-match high-precision astrometric data from Gaia DR2 with accurate multiband photometry from the Dark Energy Survey (DES) DR1 to confidently measure proper motions for nine stellar streams in the DES footprint: Aliqa Uma, ATLAS, Chenab, Elqui, Indus, Jhelum, Phoenix, Tucana III, and Turranburra. We determine low-confidence proper-motion measurements for four additional stellar streams: Ravi, Wambelong, Willka Yaku, and Turbio. We find evidence for a misalignment between stream tracks and the systemic proper motion of streams that may suggest a systematic gravitational influence from the Large Magellanic Cloud (LMC). These proper motions, when combined with radial velocity measurements, will allow for detailed orbit modeling that can be used to constrain properties of the LMC and its effect on nearby streams, as well as global properties of the Milky Way's gravitational potential.
- ID:
- ivo://CDS.VizieR/J/A+A/563/A15
- Title:
- Metallicity and kinematics in Galactic bar
- Short Name:
- J/A+A/563/A15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We observe red clump stars in four fields along the Galactic bar major axis (l=10{deg}, -6{deg}, 6{deg} and b=0{deg}, plus a field at l=0{deg}, b=1{deg}) with low-resolution spectroscopy from FLAMES/GIRAFFE (setup LR08) at the VLT, observing around the CaII triplet. We developed robust methods to extract radial velocity and metallicity estimates from these low signal-to-noise spectra. Results have been derived by fixing atmospheric parameters typical of a red clump star (Teff=4750K, logg=2.5). For some targets, the metallicity could not be derived.
- ID:
- ivo://CDS.VizieR/J/MNRAS/494/396
- Title:
- Metallicity distribution in GC
- Short Name:
- J/MNRAS/494/396
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present stellar metallicity measurements of more than 600 late-type stars in the central 10pc of the Galactic Centre. Together with our previously published KMOS data, this data set allows us to investigate, for the first time, spatial variations of the nuclear star cluster's metallicity distribution. Using the integral-field spectrograph KMOS (VLT), we observed almost half of the area enclosed by the nuclear star cluster's effective radius. We extract spectra at medium spectral resolution and apply full spectral fitting utilizing the PHOENIX library of synthetic stellar spectra. The stellar metallicities range from [M/H]=-1.25dex to [M/H]>+0.3dex, with most of the stars having supersolar metallicity. We are able to measure an anisotropy of the stellar metallicity distribution. In the Galactic north, the portion of subsolar metallicity stars with [M/H]<0.0dex is more than twice as high as in the Galactic south. One possible explanation for different fractions of subsolar metallicity stars in different parts of the cluster is a recent merger event. We propose to test this hypothesis with high- resolution spectroscopy and by combining the metallicity information with kinematic data.
- ID:
- ivo://CDS.VizieR/J/MNRAS/464/194
- Title:
- Metallicity distribution in the GC
- Short Name:
- J/MNRAS/464/194
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Knowing the metallicity distribution of stars in the Galactic Centre has important implications for the formation history of the Milky Way nuclear star cluster. However, this distribution is not well known, and is currently based on a small sample of fewer than 100 stars. We obtained near-infrared K-band spectra of more than 700 late-type stars in the central 4pc^2^ of the Milky Way nuclear star cluster with the integral-field spectrograph KMOS (VLT). We analyse the medium-resolution spectra using a full-spectral fitting method employing the Gottingen spectral library of synthetic PHOENIX spectra. The derived stellar metallicities range from metal-rich [M/H]>+0.3dex to metal-poor [M/H]<-1.0dex, with a fraction of 5.2^+6.0^_-3.1_ per cent metal-poor ([M/H]<=-0.5dex) stars. The metal-poor stars are distributed over the entire observed field. The origin of metal-poor stars remains unclear. They could originate from infalling globular clusters. For the metal-rich stellar population ([M/H]>0dex), a globular cluster origin can be ruled out. As there is only a very low fraction of metal-poor stars in the central 4pc^2^ of the Galactic Centre, we believe that our data can discard a scenario in which the Milky Way nuclear star cluster is purely formed from infalling globular clusters.
- ID:
- ivo://CDS.VizieR/J/ApJ/703/2177
- Title:
- Metal-poor MS turnoff stars summary
- Short Name:
- J/ApJ/703/2177
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We identify 10 -- seven for the first time -- elements of cold halo substructure (ECHOS) in the volume within 17.5kpc of the Sun in the inner halo of the Milky Way. Our result is based on the observed spatial and radial velocity distribution of metal-poor main-sequence turnoff (MPMSTO) stars in 137 Sloan Extension for Galactic Understanding and Exploration lines of sight. We show that all of our detections are statistically significant and that we expect no false positives. These ECHOS represent the observable stellar debris of ancient merger events in the stellar accretion history of the Milky Way, and we use our detections and completeness estimates to infer a formal upper limit of 0.34^+0.02^_-0.02_ on the fraction of the MPMSTO population in the inner halo that belong to ECHOS.
