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2811. CH_3_OH and H_2_O Galactic center masers
ID:
ivo://CDS.VizieR/J/A+A/563/A68
Title:
CH_3_OH and H_2_O Galactic center masers
Short Name:
J/A+A/563/A68
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a study of star formation in the central molecular zone (CMZ) of our Galaxy through the association of three star formation indicators: 6.7GHz CH_3_OH masers, 22GHz H_2_O masers, and enhanced 4.5{mu}m emission ('green') sources. We explore how star formation in the CMZ (|l|<1.3{deg}, |b|<10') compares with that of the Galactic disk (6{deg}>l>345{deg}, |b|<2{deg}). Using an automated algorithm, we search for green sources toward 6.7GHz CH_3_OH masers detected in the Parkes Methanol Multibeam Survey. We combine these results with lists of 22GHz H_2_O masers, including our Mopra survey of the CMZ. We find that the correlation of CH_3_OH masers with green sources is a function of Galactic latitude, with a minimum close to b=0 and increasing with |b| (toward the central part of the Galaxy, 6{deg}>l>345{deg}, |b|<2{deg}). We find no significant difference between the correlation rate of CH_3_OH masers with green sources in the CMZ and the disk. This suggests that although the physical conditions of the gas are different in the CMZ from that of the Galactic disk, once gravitational instability sets in at sufficiently high densities, signatures of star formation appear to be similar in both regions. Moreover, the detection of green sources, even at the distance of the Galactic center, shows that our technique can easily identify the early stages of star formation, especially in low-extinction regions of the Galaxy. Through the association of H_2_O and CH_3_OH masers, we identify 15 star-forming sites in the CMZ. We find a higher correlation rate of coincident H_2_O and CH_3_OH masers within the CMZ compared to the Galactic disk, indicating a difference in the maser evolutionary sequence for star-forming cores in these two regions.
2812. CH3OH in the HD100546 disk
ID:
ivo://CDS.VizieR/J/other/NatAs/5.684
Title:
CH3OH in the HD100546 disk
Short Name:
J/other/NatAs/5.
Date:
17 Jan 2022 00:30:51
Publisher:
CDS
Description:
Quantifying the composition of the material in protoplanetary disks is paramount to determining the potential for exoplanetary systems to produce and support habitable environments. When considering potential habitability, complex organic molecules are of relevance, key among which is methanol (CH_3_OH). Methanol primarily forms at low temperatures via the hydrogenation of CO ice on the surface of icy dust grains and is a necessary basis for the formation of more complex species such as amino acids and proteins. We report the detection of CH_3_OH in a disk around a young, luminous A-type star, HD 100546. This disk is warm and therefore does not host an abundant reservoir of CO ice. We argue that the CH_3_OH cannot form in situ, and hence this disk has probably inherited complex-organic-molecule-rich ice from an earlier cold dark cloud phase. This is strong evidence that at least some interstellar organic material survives the disk formation process and can then be incorporated into forming planets, moons and comets. Therefore, crucial pre-biotic chemical evolution already takes place in dark star-forming clouds.
2813. CH_3_OH maser sources
ID:
ivo://CDS.VizieR/J/other/RAA/10.67
Title:
CH_3_OH maser sources
Short Name:
J/other/RAA/10.6
Date:
21 Oct 2021
Publisher:
CDS
Description:
Using the 13.7m telescope of the Purple Mountain Observatory (PMO), a survey of the J=1-0 lines of CO and its isotopes was carried out on 98 methanol maser sources in January 2008. Eighty-five sources have infrared counterparts within one arcmin.
2814. CH_3_OH maser survey of EGOs
ID:
ivo://CDS.VizieR/J/ApJ/702/1615
Title:
CH_3_OH maser survey of EGOs
Short Name:
J/ApJ/702/1615
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of a high angular resolution Very Large Array (VLA) Class I 44GHz and Class II 6.7GHz CH_3_OH maser survey of a sample of ~20 massive young stellar object (MYSO) outflow candidates selected on the basis of extended 4.5um emission in Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire images. These 4.5um selected candidates are referred to as extended green objects (EGOs), for the common coding of this band as green in three-color Infrared Array Camera images. The detection rate of 6.7GHz Class II CH_3_OH masers, which are associated exclusively with massive YSOs, toward EGOs is >~64% - nearly double the detection rate of surveys using other MYSO selection criteria. The detection rate of Class I 44GHz CH_3_OH masers, which trace molecular outflows, is ~89% toward EGOs associated with 6.7GHz CH_3_OH masers.
2815. CH_3_OH & OH line emission from Galactic center
ID:
ivo://CDS.VizieR/J/ApJS/227/10
Title:
CH_3_OH & OH line emission from Galactic center
Short Name:
J/ApJS/227/10
Date:
21 Oct 2021
Publisher:
CDS
Description:
Class I methanol masers are collisionally pumped and are generally correlated with outflows in star-forming sites in the Galaxy. Using the Very Large Array in its A-array configuration, we present a spectral line survey to identify methanol J=4_-1_->3_0_E emission at 36.169GHz. Over 900 pointings were used to cover a region 66'x13' along the inner Galactic plane. A shallow survey of OH at 1612, 1665, 1667, and 1720MHz was also carried out over the area covered by our methanol survey. We provide a catalog of 2240 methanol masers with narrow line-widths of ~1km/s, spatial resolutions of ~0.14"x0.05", and rms noises ~20mJy/beam per channel. Lower limits on the brightness temperature range from 27000 to 10000000K, showing that the emission is of non-thermal origin. We also provide a list of 23 OH (1612), 14 OH (1665), 5 OH (1667), and 5 OH (1720MHz) masers. The origin of such a large number of methanol masers is not clear. Many methanol masers appear to be associated with infrared dark clouds, though it appears unlikely that the entire population of these masers traces the early phase of star formation in the Galactic center.
2816. Choirs, HI galaxy groups
ID:
ivo://CDS.VizieR/J/MNRAS/433/543
Title:
Choirs, HI galaxy groups
Short Name:
J/MNRAS/433/543
Date:
21 Oct 2021
Publisher:
CDS
Description:
H{alpha} observations centred on galaxies selected from the Hi Parkes All-Sky Survey (HiPASS) typically show one and sometimes two star-forming galaxies within the ~15arcmin beam of the Parkes 64m HI detections. In our Survey for Ionization in Neutral Gas Galaxies (SINGG) we found 15 cases of HiPASS sources containing four or more emission line galaxies (ELGs). We name these fields Choir groups. In the most extreme case, we found a field with at least nine ELGs. In this paper, we present a catalogue of Choir group members in the context of the wider SINGG sample. The dwarf galaxies in the Choir groups would not be individually detectable in HiPASS at the observed distances if they were isolated, but are detected in SINGG narrow-band imaging due to their membership of groups with sufficiently large total HI mass. The ELGs in these groups are similar to the wider SINGG sample in terms of size, H{alpha} equivalent width and surface brightness. Eight of these groups have two large spiral galaxies with several dwarf galaxies and may be thought of as morphological analogues of the Local Group. However, on average our groups are not significantly Hi deficient, suggesting that they are at an early stage of assembly, and more like the M81 group. The Choir groups are very compact at typically only 190kpc in projected distance between the two brightest members. They are very similar to SINGG fields in terms of star formation efficiency (SFE; the ratio of star formation rate to HI mass), showing an increasing trend in SFE with stellar mass.
2817. Chromospheric activity-age relation
ID:
ivo://CDS.VizieR/J/MNRAS/298/332
Title:
Chromospheric activity-age relation
Short Name:
J/MNRAS/298/332
Date:
21 Oct 2021
Publisher:
CDS
Description:
We show that there is a relationship between the age excess, defined as the difference between the stellar isochrone and chromospheric ages, and the metallicity as measured by the index [Fe/H] for late-type dwarfs. The chromospheric age tends to be lower than the isochrone age for metal-poor stars, and the opposite occurs for metal-rich objects. We suggest that this could be an effect of neglecting the metallicity dependence of the calibrated chromospheric emission-age relation. We propose a correction to account for this dependence. We also investigate the metallicity distributions of these stars, and show that there are distinct trends according to the chromospheric activity level. Inactive stars have a metallicity distribution which resembles the metallicity distribution of solar neighbourhood stars, while active stars appear to be concentrated in an activity strip on the log(R'_HK_)*[Fe/H] diagram. We provide some explanations for these trends, and show that the chromospheric emission-age relation probably has different slopes on the two sides of the Vaughan-Preston gap.
2818. Chromospheric activity for CPS stars
ID:
ivo://CDS.VizieR/J/ApJ/725/875
Title:
Chromospheric activity for CPS stars
Short Name:
J/ApJ/725/875
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present time series measurements of chromospheric activity for more than 2600 main-sequence and subgiant stars on the California Planet Search (CPS) program with spectral types ranging from about F5V to M4V for main-sequence stars and from G0IV to about K5IV for subgiants. The large data set of more than 44000 spectra allows us to identify an empirical baseline floor for chromospheric activity as a function of color and height above the main sequence. We define {Delta}S as an excess in emission in the CaII H and K lines above the baseline activity floor and define radial velocity jitter as a function of {Delta}S and B-V for main-sequence and subgiant stars. Although the jitter for any individual star can always exceed the baseline level, we find that K dwarfs have the lowest level of jitter. The lack of correlation between observed jitter and chromospheric activity in K dwarfs suggests that the observed jitter is dominated by instrumental or analysis errors and not astrophysical noise sources. Thus, given the long-term precision for the CPS program, radial velocities are not correlated with astrophysical noise for chromospherically quiet K dwarf stars, making these stars particularly well suited for the highest precision Doppler surveys. Chromospherically quiet F and G dwarfs and subgiants exhibit higher baseline levels of astrophysical jitter than K dwarfs. Despite the fact that the rms in Doppler velocities is correlated with the mean chromospheric activity, it is rare to see one-to-one correlations between the individual time series activity and Doppler measurements, diminishing the prospects for correcting activity-induced velocity variations in F and G dwarfs.
2819. Chromospheric activity from AMBRE-HARPS
ID:
ivo://CDS.VizieR/J/A+A/646/A77
Title:
Chromospheric activity from AMBRE-HARPS
Short Name:
J/A+A/646/A77
Date:
21 Oct 2021
Publisher:
CDS
Description:
The main objective of this project is to characterise chromospheric activity of FGK stars from the HARPS archive. We start, in this first paper, by presenting a catalogue of homogeneous determined chromospheric emission (CE), stellar atmospheric parameters and ages for 1,674 FGK main sequence (MS), subgiant, and giant stars. The analysis of CE level and variability is also performed. We measured CE in the CaII lines using more than 180000 high-resolution spectra from the HARPS spectrograph, as compiled in the AMBRE project, obtained between 2003 and 2019. We converted the fluxes to bolometric and photospheric corrected chromospheric emission ratio, R'_HK_. Stellar atmospheric parameters T_eff_, logg, and [Fe/H] were retrieved from the literature or determined using an homogeneous method. M_{star}_, R_{star}_, and ages were determined from isochrone fitting. We show that our sample has a distribution of CE for MS stars that is consistent with an unbiased sample of solar-neighbour MS stars. We analysed the CE distribution for the different luminosity classes and spectral types and confirmed the existence of the very inactive stars (VIS) and very active stars (VAS) populations at R'_HK_<-5.1 and >-4.2dex, respectively. We found indications that the VIS population is composed mainly of subgiant and giant stars and that R'_HK_=-5.1dex marks a transition in stellar evolution. Overall, CE variability decreases with decreasing CE level but its distribution is complex. There appears to be at least three regimes of variability, for inactive, active and very active stars, with the inactive and active regimes separated by a diagonal, extended Vaughan-Preston (VP) gap. We show that stars with low activity levels do not necessarily have low variability. In the case of K dwarfs which show high CE variability, inactive and active stars have similar levels of activity variability. This means that activity levels alone are not enough to infer about the activity variability of a star. We also explained the shape of the VP gap observed in the distribution of CE by using the CE variability-level diagram. In the CE variability-level diagram, the Sun is located in the high variability region of the inactive MS stars zone. A method to extract the probability density function of the CE variability for a given R'_HK_ level is discussed, and a python code to retrieve it is provided.
2820. Chromospheric activity in late-type stars
ID:
ivo://CDS.VizieR/J/A+A/469/309
Title:
Chromospheric activity in late-type stars
Short Name:
J/A+A/469/309
Date:
21 Oct 2021
Publisher:
CDS
Description:
The main chromospheric activity indicator is the S index, which is the ratio of the flux in the core of the CaII H and K lines to the continuum nearby, and is well studied for stars from F to K. Another chromospheric proxy is the Halpha line, which is believed to be tightly correlated with the CaII index. In this work we characterize both chromospheric activity indicators, the one associated with the H and K CaII lines and the other with Halpha, for the whole range of late type stars, from F to M.

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