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- ID:
- ivo://CDS.VizieR/J/A+A/486/9
- Title:
- Redshifts in z~0.25 clusters
- Short Name:
- J/A+A/486/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the relation between star-formation activity and environment in six intermediate redshift clusters (z~0.25) out to large clustercentric distances (~4R_vir_). For that, we conducted a panoramic spectroscopic campaign with MOSCA at the Calar Alto observatory. We acquired spectra of more than 500 objects. Approximately 150 of these spectra were of galaxies that are members of the clusters. Other ~150 are field galaxies or galaxies belonging to groups, serendipitously found during the investigation. The rest of the spectra did not met the quality criteria or were stars. The wavelength range allows us to quantify the star formation activity by using the [OII] and the H{alpha} lines. This activity is examined in terms of the large-scale environment expressed by the clustercentric distance of the galaxies as well as on local scales given by the spatial galaxy densities. The suppression of the star-formation activity is observed at large clustercentric distances and low projected densities. Galaxies with current star-formation show similar activity, regardless of the environment, Therefore, the decline of the star-formation activity inside the investigated clusters is driven mainly by the significant change in the fraction of active versus passive populations. This suggests that the suppression of the star-formation activity occurs on short timescales. We also detect a significant population of red star-forming galaxies whose colors are consistent with the red-sequence of passive galaxies. They appear to be in an intermediate evolutionary stage between active and passive types.
- ID:
- ivo://CDS.VizieR/J/AJ/123/100
- Title:
- Redshifts of AWM and MKW poor clusters
- Short Name:
- J/AJ/123/100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have measured 1365 redshifts to a limiting magnitude of R~15.5 in 15 AWM/MKW clusters and have collected another 203 from the literature in MKW 4s, MKW 2, and MKW 2s. In AWM 7 we have extended the redshift sample to R~18 in the cluster center. We have identified 704 cluster members in 17 clusters; 201 are newly identified. We summarize the kinematics and distributions of the cluster galaxies and provide an initial discussion of substructure, mass and luminosity segregation, spectral segregation, velocity-dispersion profiles, and the relation of the central galaxy to global cluster properties. We compute optical mass estimates, which we compare with X-ray mass determinations from the literature.
- ID:
- ivo://CDS.VizieR/J/ApJ/886/42
- Title:
- Reverberation mapping & opt. spectra data of AGNs
- Short Name:
- J/ApJ/886/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The radius-luminosity (R_H{beta}_-L_5100_) relationship of active galactic nuclei (AGNs) established by the reverberation mapping (RM) observations has been widely used as a single-epoch black hole mass estimator in the research of large AGN samples. However, the recent RM campaigns discovered that the AGNs with high-accretion rates show shorter time lags by factors of a few comparing with the predictions from the R_H{beta}_-L_5100_ relationship. The explanation of the shortened time lags has not been finalized yet. We collect eight different single-epoch spectral properties to investigate how the shortening of the time lags correlates with those properties and to determine the origin of the shortened lags. We find that the flux ratio between FeII and H{beta} emission lines shows the most prominent correlation, thus confirming that accretion rate is the main driver for the shortened lags. In addition, we establish a new scaling relation including the relative strength of FeII emission. This new scaling relation can provide less biased estimates of the black hole mass and accretion rate from the single-epoch spectra of AGNs.
- ID:
- ivo://CDS.VizieR/J/AJ/155/71
- Title:
- RGB & HB members of the bulge cluster NGC 6569
- Short Name:
- J/AJ/155/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photometric and spectroscopic analyses have shown that the Galactic bulge cluster Terzan 5 hosts several populations with different metallicities and ages that manifest as a double red horizontal branch (HB). A recent investigation of the massive bulge cluster NGC 6569 revealed a similar, though less extended, HB luminosity split, but little is known about the cluster's detailed chemical composition. Therefore, we have used high-resolution spectra from the Magellan-M2FS and VLT-FLAMES spectrographs to investigate the chemical compositions and radial velocity distributions of red giant branch and HB stars in NGC 6569. We found the cluster to have a mean heliocentric radial velocity of -48.8 km/s ({sigma}=5.3 km/s; 148 stars) and <[Fe/H]>=-0.87 dex (19 stars), but the cluster's 0.05 dex [Fe/H] dispersion precludes a significant metallicity spread. NGC 6569 exhibits light- and heavy-element distributions that are common among old bulge/inner Galaxy globular clusters, including clear (anti)correlations between [O/Fe], [Na/Fe], and [Al/Fe]. The light-element data suggest that NGC 6569 may be composed of at least two distinct populations, and the cluster's low <[La/Eu]>=-0.11 dex indicates significant pollution with r-process material. We confirm that both HBs contain cluster members, but metallicity and light-element variations are largely ruled out as sources for the luminosity difference. However, He mass fraction differences as small as {Delta}Y~0.02 cannot be ruled out and may be sufficient to reproduce the double HB.
- ID:
- ivo://CDS.VizieR/J/MNRAS/456/4315
- Title:
- RGB stars in NGC 6822, Ca II triplet
- Short Name:
- J/MNRAS/456/4315
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed analysis of the chemistry and kinematics of red giants in the dwarf irregular galaxy NGC 6822. Spectroscopy at ~8500{AA} was acquired for 72 red giant stars across two fields using FORS2 at the VLT. Line-of-sight extinction was individually estimated for each target star to accommodate the variable reddening across NGC 6822. The mean radial velocity was found to be <v_rad_>=-52.8+/-2.2km/s with dispersion {sigma}_v_=24.1km/s, in agreement with other studies. Ca ii triplet equivalent widths were converted into [Fe/H] metallicities using a V magnitude proxy for surface gravity. The average metallicity was <[Fe/H]>=-0.84+/-0.04 with dispersion {sigma}=0.31dex and interquartile range 0.48. Our assignment of individual reddening values makes our analysis more sensitive to spatial variations in metallicity than previous studies. We divide our sample into metal-rich and metal-poor stars; the former were found to cluster towards small radii with the metal-poor stars more evenly distributed across the galaxy. The velocity dispersion of the metal-poor stars was found to be higher than that of the metal-rich stars {sigma}_vMP_=27.4km/s; {sigma}_vMR_=21.1km/s); combined with the age-metallicity relation this indicates that the older populations have either been dynamically heated during their lifetimes or were born in a less disc-like distribution than the younger stars.. The low ratio v_rot_/{sigma}_v_ suggests that within the inner 10-arcmin, NGC 6822's stars are dynamically decoupled from the HI gas, and possibly distributed in a thick disc or spheroid structure.
- ID:
- ivo://CDS.VizieR/J/A+A/353/1044
- Title:
- ROSAT obs. of T Tauri stars in MBM 12
- Short Name:
- J/A+A/353/1044
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the ROSAT PSPC pointed and ROSAT All-Sky Survey (RASS, Cat. <IX/10>) observations and the results of our low and high spectral resolution optical follow-up observations of the T Tauri stars (TTS) and X-ray selected T Tauri star candidates in the region of the high galactic latitude dark cloud MBM 12 (L1453-L1454, L1457, L1458). Table 4 lists all of the X-ray detected sources in the direction of the molecular cloud MBM12 along with relevant X-ray and optical data.
- ID:
- ivo://CDS.VizieR/J/ApJ/837/96
- Title:
- Rotation-Activity Correlations in K-M dwarfs II.
- Short Name:
- J/ApJ/837/96
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the rotation-activity correlations (RACs) in a sample of stars from spectral type dK4 to dM4. We study RACs using chromospheric data and coronal data. We study the Ca II line surface fluxes-P/sini RACs. We fit the RACs with linear homoscedastic and heteroscedastic regression models. We find that these RACs differ substantially from one spectral sub-type to another. For dM3 and dM4 stars, we find that the RACs cannot be described by a simple model, but instead that there may exist two distinct RAC behaviors for the low-activity and the high-activity stellar sub-samples, respectively. Although these results are preliminary and will need confirmation, the data suggest that these distinct RACs may be associated with different dynamo regimes. We also study R'_HK_ as a function of the Rossby number R_0_. We find (i) for dK4 stars, R'_HK_ as a function of R_0_ agrees well with previous results for F-G-K stars and (ii) in dK6, dM2, dM3, and dM4 stars, at a given R_0_, the values of R'_HK_ lie at a factor of 3, 10, 20, and 90, respectively, below the F-G-K RAC. Our results suggest a significant decrease in the efficiency of the dynamo mechanism(s) as regards chromospheric heating before and at dM3, i.e., before and at the transition to complete convection. We also show that the ratio of coronal heating to chromospheric heating L_X_/L_HK_ increases by a factor of 100 between dK4 and dM4 stars.
- ID:
- ivo://CDS.VizieR/J/AJ/117/2941
- Title:
- Rotation periods of Orion PMS stars
- Short Name:
- J/AJ/117/2941
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report rotation periods for 254 stars in an area 40'x80' centered on the Orion Nebula. We show that these stars are likely members of the young (~10^6^yr) Orion OBIc/d association. The rotation period distribution we determine, which is sensitive to periods 0.1<P<8days, shows a sharp cutoff for periods P<0.5days, corresponding to breakup velocity for these stars. Above 0.5days the distribution is consistent with a uniform distribution; we do not find evidence for a "gap" of periods at 4-5days. We find signatures of active accretion among stars at all periods; active accretion does not occur preferentially among slow rotators in our sample. We find no correlation between rotation period and near-IR signatures of circumstellar disks. In addition, we show that the distribution of vsini among stars in our sample bears striking resemblance to that of low-mass Pleiades stars. We discuss the implications of our findings for the evolution of stellar angular momentum during the pre-main-sequence phase. We argue that all stars in our sample must still deplete angular momentum by factors of roughly 5-10, if they are to preserve their vsini distribution over approximately the next 100Myr. We consider in detail whether our findings are consistent with disk-regulated stellar rotation. We do not find observational evidence that magnetic disk-locking is the dominant mechanism in angular momentum evolution during the premain-sequence phase.
- ID:
- ivo://CDS.VizieR/J/ApJ/858/92
- Title:
- RPA Southern Pilot Search of 107 Stars
- Short Name:
- J/ApJ/858/92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The recent detection of a binary neutron star merger and the clear evidence for the decay of radioactive material observed in this event have, after 60 years of effort, provided an astrophysical site for the rapid neutron- capture (r-) process which is responsible for the production of the heaviest elements in our universe. However, observations of metal-poor stars with highly-enhanced r-process elements have revealed abundance patterns suggesting that multiple sites may be involved. To address this issue and to advance our understanding of the r-process, we have initiated an extensive search for bright (V<13.5), very metal-poor ([Fe/H]<-2) stars in the Milky Way halo exhibiting strongly-enhanced r-process signatures. This paper presents the first sample collected in the southern hemisphere using the echelle spectrograph on du Pont 2.5m telescope at Las Campanas Observatory. We have observed and analyzed 107 stars with -3.13<[Fe/H]<-0.79. Of those, 12 stars are strongly enhanced in heavy r-process elements (r-II), 42 stars show moderate enhancements of heavy r-process material (r-I), and 20 stars exhibit low abundances of the heavy r-process elements and higher abundances of the light r-process elements relative to the heavy ones (limited-r). This search is more successful at finding r- process-enhanced stars compared to previous searches, primarily due to a refined target-selection procedure.
