- ID:
- ivo://CDS.VizieR/J/ApJ/770/16
- Title:
- Spectroscopic members of Segue 2 galaxy
- Short Name:
- J/ApJ/770/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Segue 2, discovered by Belokurov et al. (2009, Cat. J/MNRAS/397/1748), is a galaxy with a luminosity of only 900L_{sun}_. We present Keck/DEIMOS spectroscopy of 25 members of Segue 2 - a threefold increase in spectroscopic sample size. The velocity dispersion is too small to be measured with our data. The upper limit with 90% (95%) confidence is {sigma}_v_<2.2(2.6)km/s, the most stringent limit for any galaxy. The corresponding limit on the mass within the three-dimensional half-light radius (46pc) is M_1/2_<1.5(2.1)x10^5^M_{sun}_. Segue 2 is the least massive galaxy known. We identify Segue 2 as a galaxy rather than a star cluster based on the wide dispersion in [Fe/H] (from -2.85 to -1.33) among the member stars. The stars' [{alpha}/Fe] ratios decline with increasing [Fe/H], indicating that Segue 2 retained Type Ia supernova ejecta despite its presently small mass and that star formation lasted for at least 100 Myr. The mean metallicity, <[Fe/H]>=-2.22+/-0.13 (about the same as the Ursa Minor galaxy, 330 times more luminous than Segue 2), is higher than expected from the luminosity-metallicity relation defined by more luminous dwarf galaxy satellites of the Milky Way. Segue 2 may be the barest remnant of a tidally stripped, Ursa Minor-sized galaxy. If so, it is the best example of an ultra-faint dwarf galaxy that came to be ultra-faint through tidal stripping. Alternatively, Segue 2 could have been born in a very low mass dark matter subhalo (v_max_<10km/s), below the atomic hydrogen cooling limit.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/902/42
- Title:
- Spectroscopic monitoring of blazar S5 0716+714
- Short Name:
- J/ApJ/902/42
- Date:
- 10 Mar 2022 15:02:00
- Publisher:
- CDS
- Description:
- In this paper, we report new results of spectroscopic observations of {gamma}-ray blazar S5 0716+714 from 2019 September to 2020 March with the 2.4m optical telescope at Lijiang Observatory of Yunnan Observatories. The median cadence of observations is ~1 day. During the second observation period (Epoch2), the observational data reveal an extremely bright state and a bluer-when-brighter (BWB) chromatism. The BWB trend of Epoch2 differs significantly from that of the first observation period (Epoch1). A significantly brightness-dependent BWB chromatism emerges in the total data of Epoch1 and Epoch2. The BWB trend becomes weaker toward the brighter states, and likely becomes saturated at the highest state. Based on a log-parabolic function, a power law of synchrotron peak flux and frequency {nu}p, and a power law of the curvature of synchrotron spectrum and its {nu}p, simulation well reproduces the brightness-dependent BWB trend of S5 0716+714. The BWB trend is seemingly controlled by the shift of {nu}p with respect to the observational window, and effectively may be dominated by the variations of electron average energy and magnetic field in the emitting region.
- ID:
- ivo://CDS.VizieR/J/A+A/473/523
- Title:
- Spectroscopic monitoring of 3 neutron stars
- Short Name:
- J/A+A/473/523
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a spectroscopic monitoring campaign of the OB-star companions to the eclipsing X-ray pulsars SMC X-1, LMC X-4 and Cen X-3. High-resolution optical spectra obtained with UVES on the ESO Very Large Telescope are used to determine the radial-velocity orbit of the OB (super)giants with high precision. The excellent quality of the spectra provides the opportunity to measure the radial-velocity curve based on individual lines, and to study the effect of possible distortions of the line profiles due to e.g. X-ray heating on the derived radial-velocity amplitude.
- ID:
- ivo://CDS.VizieR/J/ApJ/751/46
- Title:
- Spectroscopic observations in VV124 (UGC 4879)
- Short Name:
- J/ApJ/751/46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- VV124 (UGC 4879) is an isolated, dwarf irregular/dwarf spheroidal (dIrr/dSph) transition-type galaxy at a distance of 1.36 Mpc. Previous low-resolution spectroscopy yielded inconsistent radial velocities for different components of the galaxy, and photometry hinted at the presence of a stellar disk. In order to quantify the stellar dynamics, we observed individual red giants in VV124 with the Keck/Deep Extragalactic Imaging Multi-Object Spectrograph (DEIMOS). We validated members based on their positions in the color-magnitude diagram, radial velocities, and spectral features. Our sample contains 67 members. The average radial velocity is <v_r_>=-29.1+/-1.3km/s in agreement with the previous radio measurements of H I gas. The velocity distribution is Gaussian, indicating that VV124 is supported primarily by velocity dispersion inside a radius of 1.5 kpc. Outside that radius, our measurements provide only an upper limit of 8.6km/s on any rotation in the photometric disk-like feature. The velocity dispersion is {sigma}_v_=9.4+/-1.0km/s, from which we inferred a mass of M_1/2_=(2.1 +/-0.2)x10^7^M_{sun}_ and a mass-to-light ratio of (M/L_V_)_1/2_=5.2+/-1.1M_{sun}_/L_{sun}_, both measured within the half-light radius. Thus, VV124 contains dark matter. We also measured the metallicity distribution from neutral iron lines. The average metallicity, <[Fe/H]>=-1.14+/-0.06, is consistent with the mass-metallicity relation defined by dSph galaxies. The dynamics and metallicity distribution of VV124 appear similar to dSphs of similar stellar mass.
- ID:
- ivo://CDS.VizieR/J/A+AS/101/475
- Title:
- Spectroscopic observations of A3571
- Short Name:
- J/A+AS/101/475
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectroscopic data and density counts are presented for this southern cluster, which seems to belong to the outskirts of the Shapley 8 concentration (= A 3558 = SC 1326-311). Using telescopes at the Cerro Tololo Interamerican Observatory and La Silla Observatory a total of 72 galaxy velocities were measured giving a mean redshift of 0.0384 and a global velocity dispersion of 1022 (+99, -77) km/s. A preliminary analysis of velocity and density data suggests the presence of various subgroups. The central core of the cluster is dominated by a very elongated, distorded and diffuse cD galaxy. This cluster may be an example where the cD was formed early in the collapse process of a cluster which has not reached overall virialization yet. The derived X-ray luminosity of ~2x10^44^erg/s in the 2-6keV band places this cluster in the group of strong X-ray cluster sources.
- ID:
- ivo://CDS.VizieR/J/A+A/408/305
- Title:
- Spectroscopic observations of delta Sco
- Short Name:
- J/A+A/408/305
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a spectroscopic monitoring program of the binary system Scorpii, whose primary became a Be star after the last periastron encounter in the Summer of 2000. The observations cover a period of 2 years (March 2001-June 2003) and are a continuation of our previous campaign reported in Miroshnichenko et al. (2001A&A...377..485M). We found that the emission-line spectrum was gradually strengthening over the whole monitoring period. Several short-term increases of the line emission, possibly due to outbursts of matter ejected from the stellar surface, were detected. The outbursts seem to be responsible for the brightness fadings, seen afterwards. We attempt to explain the overall observed line and continuum behaviour in terms of a circumstellar disk, growing in density and size. The disk is most likely Keplerian with an outer radius of and a mean expansion speed of ~0.4km/s.
- ID:
- ivo://CDS.VizieR/J/MNRAS/405/839
- Title:
- Spectroscopic observations of globular clusters
- Short Name:
- J/MNRAS/405/839
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of medium-resolution spectroscopy of 28 globular clusters (GCs) in six nearby galaxies of different luminosities and morphological types, situated in M33 (15 objects), M31 (three), IC10 (four), UGCA86 (four), Holmberg IX (one) and DDO71 (one) obtained at the Special Astrophysical Observatory 6-m telescope. Measurements of Lick absorption line indices and comparison with Simple Stellar Population models enabled us to obtain their spectroscopic ages, metallicities and {alpha}-element to Fe abundance ratios.
- ID:
- ivo://CDS.VizieR/J/A+A/501/291
- Title:
- Spectroscopic observations of HD 152219
- Short Name:
- J/A+A/501/291
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- HD 152219 is a massive binary system with O9.5 III + B1-2 V/III components and a short orbital period of 4.2d. Its primary component further displays clear line profile variability (LPV). The primary component being located within the pulsational instability domain predicted for high-luminosity stars, we previously suggested that the observed LPV could be associated with non-radial pulsations. The aim of the present work is to determine the nature of the observed LPV in the spectrum of the primary component of HD 152219. During a 4-night FEROS monitoring campaign, we collected a new set of 134 high signal-to-noise spectra. These new observations were then used to re-investigate the variability of different line profiles in the spectrum of HD~152219. Based on the present analysis, we discard the non-radial pulsations and point out the Rossiter-McLaughlin effect as the cause of the LPV in HD 152219. The upper limit on the amplitude of possible weak pulsations is set at a few parts per thousand of the continuum level.
- ID:
- ivo://CDS.VizieR/J/ApJ/653/657
- Title:
- Spectroscopic observations of Herbig Ae/Be stars
- Short Name:
- J/ApJ/653/657
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present optical spectra of 45 intermediate-mass Herbig Ae/Be stars. Together with the multiepoch spectroscopic and photometric data compiled for a large sample of these stars and ages estimated for individual stars by using pre-main-sequence evolutionary tracks, we have studied the evolution of emission-line activity in them. We find that, on average, the H{alpha} emission line strength decreases with increasing stellar age in Herbig Ae/Be stars, indicating that the accretion activity gradually declines during the pre-main-sequence phase.
- ID:
- ivo://CDS.VizieR/J/PAZh/32/628
- Title:
- Spectroscopic observations of southern stars
- Short Name:
- J/PAZh/32/628
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of spectrophotometric observations of 64 southern stars in the range from 320 to 730nm are presented as quasi-monochromatic luminosities from the stars on the external board of atmosphere expressed in the absolute energy units (W/m^2^/m) with spectral interval of 2.5nm.