- ID:
- ivo://CDS.VizieR/J/MNRAS/442/1663
- Title:
- Velocities of red giants in the SMC
- Short Name:
- J/MNRAS/442/1663
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from an extensive spectroscopic survey of field stars in the Small Magellanic Cloud (SMC). 3037 sources, predominantly first-ascent red giants, spread across roughly 37.5deg^2^, are analysed. The line-of-sight velocity field is dominated by the projection of the orbital motion of the SMC around the Large Magellanic Cloud/Milky Way. The residuals are inconsistent with both a non-rotating spheroid and a nearly face on disc system. The current sample and previous stellar and Hi kinematics can be reconciled by rotating disc models with line-of-nodes position angle {Theta} ~120{deg}-130{deg}, moderate inclination (25{deg}-70{deg}), and rotation curves rising at 20-40km/s/kpc. The metal-poor stars exhibit a lower velocity gradient and higher velocity dispersion than the metal-rich stars. If our interpretation of the velocity patterns as bulk rotation is appropriate, then some revision to simulations of the SMC orbit is required since these are generally tuned to the SMC disc line of nodes lying in a north-east-south-west (SW) direction. Residuals show strong spatial structure indicative of non-circular motions that increase in importance with increasing distance from the SMC centre. Kinematic substructure in the north-west part of our survey area is associated with the tidal tail or Counter-Bridge predicted by simulations. Lower line-of-sight velocities towards the Wing and the larger velocities just beyond the SW end of the SMC Bar are probably associated with stellar components of the Magellanic-Bridge and Counter-Bridge, respectively. Our results reinforce the notion that the intermediate-age stellar population of the SMC is subject to substantial stripping by external forces.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/153/254
- Title:
- Velocities of RGB stars in the Leo II dwarf galaxy
- Short Name:
- J/AJ/153/254
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We combine precision radial velocity data from four different published works of the stars in the Leo II dwarf spheroidal galaxy. This yields a data set that spans 19 years, has 14 different epochs of observation, and contains 372 unique red giant branch stars, 196 of which have repeat observations. Using this multi-epoch data set, we constrain the binary fraction for Leo II. We generate a suite of Monte Carlo simulations that test different binary fractions using Bayesian analysis and determine that the binary fraction for Leo II ranges from 0.30_-0.10_^+0.09^ to 0.34_-0.11_^+0.11^, depending on the distributions of binary orbital parameters assumed. This value is smaller than what has been found for the solar neighborhood (~0.4-0.6) but falls within the wide range of values that have been inferred for other dwarf spheroidals (0.14-0.69). The distribution of orbital periods has the greatest impact on the binary fraction results. If the fraction we find in Leo II is present in low-mass ultra-faints, it can artificially inflate the velocity dispersion of those systems and cause them to appear more dark matter rich than in actuality. For a galaxy with an intrinsic dispersion of 1 km/s and an observational sample of 100 stars, the dispersion can be increased by a factor of 1.5-2 for Leo II-like binary fractions or by a factor of three for binary fractions on the higher end of what has been seen in other dwarf spheroidals.
- ID:
- ivo://CDS.VizieR/J/AJ/156/300
- Title:
- Velocity and light curve analysis of three PPNe
- Short Name:
- J/AJ/156/300
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained contemporaneous light, color, and radial velocity data for three proto-planetary nebulae (PPNe) over the years 2007 to 2015. The light and velocity curves of each show similar periods of pulsation, with photometric periods of 42 and 50 days for IRAS 17436+5003, 102 days for IRAS 18095+2704, and 35 days for IRAS 19475+3119. The light and velocity curves are complex with multiple periods and small, variable amplitudes. Nevertheless, at least over limited time intervals, we were able to identify dominant periods in the light, color, and velocity curves and compare the phasing of each. The color curves appear to peak with or slightly after the light curves while the radial velocity curves peak about a quarter of a cycle before the light curves. Similar results were found previously for two other PPNe, although for them the light and color appeared to be in phase. Thus, it appears that PPNe are brightest when smallest and hottest. These phase results differ from those found for classical Cepheid variables, where the light and velocity differ by half a cycle, and are hottest at about average size and expanding. However, they do appear to have similar phasing to the larger-amplitude pulsations seen in RV Tauri variables. Presently, few pulsation models exist for PPNe, and these do not fit the observations well, especially the longer periods observed. Model fits to these new light and velocity curves would allow masses to be determined for these post-AGB objects, and thereby provide important constraints to post-AGB stellar evolution models of low- and intermediate-mass stars.
- ID:
- ivo://CDS.VizieR/J/A+A/529/A134
- Title:
- Velocity curve of {alpha} Arietis
- Short Name:
- J/A+A/529/A134
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To search for extra-solar planets around intermediate mass stars, we are conducting a precise RV survey around K-giants. We present high-accuracy RV measurements of alpha Ari from November 2003 to February 2010. This star belongs to our sample of 55 K-giants studied for extra-solar planet and pulsation searches using the fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) attached to the 1.8-m telescope at Bohyunsan Optical Astronomy Observatory (BOAO) in Korea. We find a planetary companion with a long-period and low-amplitude radial velocity (RV) variations in oscillating K2 III star alpha Ari (HD 12929). We do not find the correlation between RV variations and chromospheric activity indicators (CaII H & K region, H{alpha} line). The bisector analysis also shows that bisector velocity span (BVS) does not show any obvious correlation with RV variation but has periodic component that may be attributed to the rotation of the star. If the RV variation is indeed caused by a planetary companion, an orbital solution with a period of P=381-days, a semi-amplitude of K=41m/s, and an eccentricity of e=0.25 fits the data best. Assuming a possible stellar mass of M_star_=1.5M_{sun}_, we estimate the minimum mass for the planetary companion of m_2_sini=1.8M_{Jupiter}_ with an orbital semi-major axis of 1.2AU. Our finding of a likely exoplanet in alpha Ari gives a support to search for extra-solar planets around giant stars with multi-periodic oscillations.
- ID:
- ivo://CDS.VizieR/J/A+A/566/A67
- Title:
- Velocity curves of {beta}Cnc, {mu}Leo and {beta}UMi
- Short Name:
- J/A+A/566/A67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To investigate the low-amplitude and long-period variations in evolved stars with a precise radial velocity (RV) survey. The high-resolution, the fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) was used from 2003 to 2013 for an RV survey of giant stars as part of the exoplanet search program at Bohyunsan Optical Astronomy Observatory (BOAO). We report the detection of three new planetary companions orbiting the K giants beta Cnc, mu Leo, and beta UMi. The planetary nature of the RV variations is supported by analyses of ancillary data. The HIPPARCOS photometry shows no variations with periods close to those in RV variations and there is no strong correlation between the bisector velocity span (BVS) and the RVs for each star. Furthermore, the stars show weak or no core reversal in Ca II H lines indicating that they are inactive stars. The companion to beta Cnc has a minimum mass of 7.8M_Jup_ in a 605-day orbit with an eccentricity of 0.08. mu Leo is orbited by a companion of minimum mass of 2.4M_Jup_ having a period of 357-days, and an eccentricity of 0.09. beta UMi is a known barium star and is suspected of harbouring a white dwarf or substellar mass companion. Its companion has a minimum mass of 6.1M_Jup_, a period of 522-days, and an eccentricity e=0.19.
- ID:
- ivo://CDS.VizieR/J/A+A/608/A89
- Title:
- Very metal poor stars in MW halo
- Short Name:
- J/A+A/608/A89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the non-local thermodynamic equilibrium (NLTE) abundances of up to 10 chemical species in a sample of 59 very metal-poor (VMP, -4<=[Fe/H]<~-2) stars in seven dwarf spheroidal galaxies (dSphs) and in the Milky Way (MW) halo. Our results are based on high-resolution spectroscopic datasets and homogeneous and accurate atmospheric parameters determined in Paper I. We show that once the NLTE effects are properly taken into account, all massive galaxies in our sample, that is, the MW halo and the classical dSphs Sculptor, Ursa Minor, Sextans, and Fornax, reveal a similar plateau at [alpha/Fe]=0.3 for each of the alpha-process elements: Mg, Ca, and Ti. We put on a firm ground the evidence for a decline in alpha/Fe with increasing metallicity in the Bootes I ultra-faint dwarf galaxy (UFD), that is most probably due to the ejecta of type Ia supernovae. For Na/Fe, Na/Mg, and Al/Mg, the MW halo and all dSphs reveal indistinguishable trends with metallicity, suggesting that the processes of Na and Al synthesis are identical in all systems, independent of their mass. The dichotomy in the [Sr/Ba] versus [Ba/H] diagram is observed in the classical dSphs, similarly to the MW halo, calling for two different nucleosynthesis channels for Sr. We show that Sr in the massive galaxies is better correlated with Mg than Fe and that its origin is essentially independent of Ba, for most of the [Ba/H] range. Our three UFDs, that is Bootes I, UMa II, and Leo IV, are depleted in Sr and Ba relative to Fe and Mg, with very similar ratios of [Sr/Mg]=-1.3 and [Ba/Mg]=-1 on the entire range of their Mg abundances. The subsolar Sr/Ba ratios of Bootes I and UMa II indicate a common r-process origin of their neutron-capture elements. Sculptor remains the classical dSph, in which the evidence for inhomogeneous mixing in the early evolution stage, at [Fe/H]<-2, is the strongest.
- ID:
- ivo://CDS.VizieR/J/A+A/459/423
- Title:
- VI and [Fe/H] of Fornax dSph RGB stars
- Short Name:
- J/A+A/459/423
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the DART imaging and CaII triplet (CaT) survey of the Fornax dwarf spheroidal galaxy (dSph) at ESO. We collected hundreds of low resolution spectra of Red Giant Branch (RGB) stars in the CaT region, using VLT/FLAMES in Medusa mode, with the GIRAFFE spectrograph (grating LR8, resolving power R~6500). We list the results for the targets with a S/N per Angstrom >10 and an error in velocity <5km/s, because we found this to be the minimum for an accurate determination of velocity and equivalent width. We checked the sample to weed out any spurious object (e.g., broken fibres, background galaxies, foreground stars, spectra not consistent with RGBs). We use a 2.5sigma cut from the system velocity to derive which stars are probable velocity members of the Fornax dSph. We transform the equivalent width of the CaT lines of probable velocity members into metallicity ([Fe/H]) using the relation derived by Rutledge et al. (1997PASP..109..907R) and combining the CaT lines as in Tolstoy et al. (2001MNRAS.327..918T). The errors in [Fe/H] are based on S/N computations and adjusted to agree with repeated measurements.
- ID:
- ivo://CDS.VizieR/J/ApJ/736/24
- Title:
- VI photometry of sources in the halo of NGC253
- Short Name:
- J/ApJ/736/24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained Magellan/IMACS and HST/ACS imaging data that resolve red giant branch stars in the stellar halo of the starburst galaxy NGC 253. The HST data cover a small area, and allow us to accurately interpret the ground-based data, which cover 30% of the halo to a distance of 30kpc, allowing us to make detailed quantitative measurements of the global properties and structure of a stellar halo outside of the Local Group. The geometry of the halo is significantly flattened in the same sense as the disk, with a projected axis ratio of b/a~0.35+/-0.1. The total stellar mass of the halo is estimated to be M_halo ~2.5+/-1.5x10^9^M_{sun}_, or 6% of the total stellar mass of the galaxy, and has a projected radial dependence that follows a power law of index -2.8+/-0.6, corresponding to a three-dimensional power law index of ~-4. The total luminosity and profile shape that we measure for NGC 253 are somewhat larger and steeper than the equivalent values for the Milky Way and M31, but are well within the scatter of model predictions for the properties of stellar halos built up in a cosmological context. Structure within the halo is seen at a variety of scales: there is small kpc-scale density variation and a large shelf-like feature near the middle of the field. The techniques that have been developed will be essential for quantitatively comparing our upcoming larger sample of observed stellar halos to models of halo formation.
- ID:
- ivo://CDS.VizieR/J/A+A/427/613
- Title:
- V,i,TiOr,CN photometry of And-II AGB stars
- Short Name:
- J/A+A/427/613
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our photometric survey of Local Group galaxies, using a four filter technique based on the method of Wing (1971, Proc. Conf. Late-Type Stars, ed. G.W. Lockwood and H.M. Dyck, KPNO Contribution 554, 145) allows the identification and subsequent characterization of their late-type stellar content. Two narrow band filters centred on molecular bands of TiO and CN allow us to distinguish between AGB stars of different chemistries [M-type (O-rich) and C-type (C-rich)]. The faint dwarf spheroidal galaxy And II, a member of the M 31 subgroup, was surveyed. From photometry in V and i as well as in the narrow band filters TiO and CN we were able to identify 7 new AGB carbon stars, to derive their mean absolute <Mi> and bolometric magnitude Mbol, their luminosity function, and their spatial distribution. We are unable to establish the true C/M ratio because the few M stars of And II are overwhelmed by foreground Galactic M st
- ID:
- ivo://CDS.VizieR/J/ApJ/741/94
- Title:
- VLBA observations of H20 maser in IRAS 18286-0959
- Short Name:
- J/ApJ/741/94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of multi-epoch Very Long Baseline Array observations of the 22.2GHz H_2_O maser emission associated with the "water fountain" IRAS 18286-0959. We suggest that this object is the second example of a highly collimated bipolar precessing outflow traced by H_2_O maser emission, the other is W 43A. The detected H_2_O emission peaks are distributed over a velocity range from -50km/s to 150km/s. The spatial distribution of over 70% of the identified maser features is found to be highly collimated along a spiral jet (jet 1) extended southeast to northwest; the remaining features appear to trace another spiral jet (jet 2) with a different orientation. The two jets form a "double-helix" pattern which lies across ~200mas. The maser distribution is reasonably fit by a model consisting of two bipolar precessing jets. The three-dimensional velocities of jet 1 and jet 2 are derived to be 138km/s and 99km/s, respectively. The precession period of jet 1 is about 56 years. For jet 2, three possible models are tested and they give different values for the kinematic parameters. We propose that the appearance of two jets is the result of a single driving source with significant proper motion.
