- ID:
- ivo://CDS.VizieR/J/A+A/634/A10
- Title:
- Chemo-kinematic properties of Aquarius
- Short Name:
- J/A+A/634/A10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Dwarf galaxies found in isolation in the Local Group (LG) are unlikely to have interacted with the large LG spirals, and therefore environmental effects such as tidal and ram-pressure stripping should not be the main drivers of their evolution. We aim to provide insight into the internal mechanisms shaping LG dwarf galaxies by increasing our knowledge of the internal properties of isolated systems. Here we focus on the evolved stellar component of the Aquarius dwarf galaxy, whose kinematic and metallicity properties have only recently started to be explored. Spectroscopic data in the region of the near-infrared Ca~II triplet lines has been obtained with FORS2 at the Very Large Telescope for 53 red giant branch (RGB) stars. These data are used to derive line-of-sight velocities and [Fe/H] of the individual RGB stars. We have derived a systemic velocity of -142.2^+1.8^_-1.8_km/s, in agreement with previous determinations from both the HI gas and stars. The internal kinematics of Aquarius appears to be best modelled by a combination of random motions (l.o.s. velocity dispersion of 10.3^+1.6^_-1.3_km/s) and linear rotation (with a gradient -5.0^+1.6^_-1.9_km/s/arcmin) along a P.A.=139_-27_^+17^deg, broadly consistent with the optical projected major axis. This rotation signal is significantly misaligned or even counter-rotating to that derived from the HI gas. We also find the tentative presence of a mild negative metallicity gradient and indications that the metal-rich stars have a colder velocity dispersion than the metal-poor ones. This work represents a significant improvement with respect to previous measurements of the RGB stars of Aquarius, as it doubles the number of member stars already studied in the literature. We speculate that the misaligned rotation between the HI gas and evolved stellar component might have been the result of recent accretion of HI gas, or re-accretion after gas-loss due to internal stellar feedback.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/576/A122
- Title:
- 3C 273 high energy spectrum
- Short Name:
- J/A+A/576/A122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The high energy spectrum of 3C 273 is usually understood in terms of inverse-Compton emission in a relativistic leptonic jet. This model predicts variability patterns and delays that could be tested with simultaneous observations from the radio to the GeV range. The instruments IBIS, SPI, JEM-X on board INTEGRAL, PCA on board RXTE, and LAT on board Fermi have enough sensitivity to follow the spectral variability of 3C 273 from the keV to the GeV. We looked for correlations between the different energy bands, including radio data at 37GHz collected at the Metsahovi Radio Observatory and built quasi-simultaneous multiwavelength spectra in the high energy domain when the source is flaring either in the X-rays or in the {gamma} rays.
- ID:
- ivo://CDS.VizieR/J/A+A/544/A19
- Title:
- CH_2_NH accurate rotational rest frequencies
- Short Name:
- J/A+A/544/A19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Methanimine (CH_2_NH) has been detected in different astronomical sources, both galactic (as in several "hot cores", the circumstellar enevolope IRC+10216, and the L183 pre-stellar core) and extragalactic, and is considered a pre-biotic interstellar molecule. Its ground-state rotational spectrum has been studied in the laboratory up to 172GHz, well below the spectral ranges covered by Herschel/HIFI and the ALMA bands 9 and 10. In this laboratory study, we extend into the submillimetre-wave region the detection of the rotational spectrum of CH_2_NH in its vibrational ground state.
- 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.
- 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.
- ID:
- ivo://CDS.VizieR/J/ApJ/734/70
- Title:
- Chromospheric activity of Southern stars
- Short Name:
- J/ApJ/734/70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- I present chromospheric-activity measurements of ~670 F, G, K, and M main-sequence stars in the Southern Hemisphere, from ~8000 archival high-resolution echelle spectra taken at Las Campanas Observatory since 2004. These stars were targets from the Old Magellan Planet Search, and are now potential targets for the New Magellan Planet Search that will look for rocky and habitable planets. Activity indices (S values) are derived from CaII H and K line cores and then converted to the Mount Wilson system. From these measurements, chromospheric (log R'_HK_) indices are derived, which are then used as indicators of the level of radial-velocity jitter, age, and rotation periods these stars present.
- ID:
- ivo://CDS.VizieR/J/AJ/159/292
- Title:
- Chromospheric activity of SZ Piscium
- Short Name:
- J/AJ/159/292
- Date:
- 08 Dec 2021
- Publisher:
- CDS
- Description:
- To continue our study on chromospheric activity and detection for possible prominence events of the very active RS Canum Venaticorum star SZ Piscium (SZ Psc), long-term high-resolution spectroscopic observations were obtained during several observing runs from 2014 to 2018. Based on the spectral subtraction technique, the chromospheric emission of the CaII IRT ({lambda}8662, {lambda}8542, and {lambda}8498), H_{alpha}_, NaI D_1_, D_2_ doublet, H_{beta}_, and CaII H & K lines is mainly associated with the K1 IV primary star of the SZ Psc system, in good agreement with the previous studies, and the F8 V secondary star also shows some chromospheric emission, implying its active chromosphere. Moreover, an optical flare characterized by the HeI D3 line emission together with stronger emission in the other indicators was detected. Furthermore, two chromospheric active longitudes around the two quadratures of the system were identified for most of the time, and the chromospheric activity shows significant changes during a few orbital cycles. The chromospheric activity level seems to show a long-term variation during our observations. There were some excess absorption features in the subtracted H{alpha} line and the other activity indicators, which would be caused by prominence-like materials associated with the K1 IV primary star of the system. Prominence materials could absorb the chromospheric emission and continuum from the K1 IV primary star and even the F8 V secondary one.
- ID:
- ivo://CDS.VizieR/J/A+A/632/A60
- Title:
- CH 2THz spectra towards 7 molecular clouds
- Short Name:
- J/A+A/632/A60
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Despite being a commonly observed feature, the modification of the velocity structure in spectral line profiles by hyperfine structure complicates the interpretation of spectroscopic data. This is particularly true for observations of simple molecules such as CH and OH toward the inner Galaxy, which show a great deal of velocity crowding. In this paper, we investigate the influence of hyperfine splitting on complex spectral lines, with the aim of evaluating canonical abundances by decomposing their dependence on hyperfine structures. This is achieved from first principles through deconvolution. We present high spectral resolution observations of the rotational ground state transitions of CH near 2THz seen in absorption toward the strong FIR-continuum sources AGAL010.62-00.384, AGAL034.258+00.154, AGAL327.293- 00.579, AGAL330.954-00.182, AGAL332.826-00.549, AGAL351.581-00.352 and SgrB2(M). These were observed with the GREAT instrument on board SOFIA. The observed line profiles of CH were deconvolved from the imprint left by the lines' hyperfine structures using the Wiener filter deconvolution, an optimised kernel acting on direct deconvolution. The quantitative analysis of the deconvolved spectra first entails the computation of CH column densities. Reliable N(CH) values are of importance owing to the status of CH as a powerful tracer for H_2_ in the diffuse regions of the interstellar medium. The N(OH)/N(CH) column density ratio is found to vary within an order of magnitude with values ranging from one to 10, for the individual sources that are located outside the Galactic centre. Using CH as a surrogate for H_2_, we determined the abundance of the OH molecule to be X(OH)=1.09x10^-7^ with respect to H_2_. The radial distribution of CH column densities along the sightlines probed in this study, excluding SgrB2(M), showcase a dual peaked distribution peaking between 5 and 7 kpc. The similarity between the correspondingly derived column density profile of H_2_ with that of the CO-dark H_2_ gas traced by the cold neutral medium component of [CII] 158um emission across the Galactic plane, further emphasises the use of CH as a tracer for H_2_.
- ID:
- ivo://CDS.VizieR/J/A+A/612/A37
- Title:
- CH 149um spectra of 4 molecular clouds
- Short Name:
- J/A+A/612/A37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The methylidyne radical CH is commonly used as a proxy for molecular hydrogen in the cold, neutral phase of the interstellar medium. The optical spectroscopy of CH is limited by interstellar extinction, whereas far-infrared observations provide an integral view through the Galaxy. While the HF ground state absorption, another H_2_ proxy in diffuse gas, frequently suffers from saturation, CH remains transparent both in spiral-arm crossings and high-mass star forming regions, turning this light hydride into a universal surrogate for H_2_. However, in slow shocks and in regions dissipating turbulence its abundance is expected to be enhanced by an endothermic production path, and the idea of a "canonical" CH abundance needs to be addressed. The N=2<-1 ground state transition of CH at {lambda}149um has become accessible to high-resolution spectroscopy thanks to GREAT, the German Receiver for Astronomy at Terahertz Frequencies aboard the Stratospheric Observatory for Infrared Astronomy, SOFIA. Its unsaturated absorption and the absence of emission from the star forming regions makes it an ideal candidate for the determination of column densities with a minimum of assumptions. Here we present an analysis of four sightlines towards distant Galactic star forming regions, whose hot cores emit a strong far-infrared dust continuum serving as background signal. Moreover, if combined with the sub-millimeter line of CH at {lambda}560um, environments forming massive stars can be analyzed. For this we present a case study on the "proto-Trapezium" cluster W3 IRS5. While we confirm the global correlation between the column densities of HF and those of CH, both in arm and interarm regions, clear signposts of an over-abundance of CH are observed towards lower densities. However, a significant correlation between the column densities of CH and HF remains. A characterization of the hot cores in the W3 IRS5 proto-cluster and its envelope demonstrates that the sub-millimeter/far-infrared lines of CH reliably trace not only diffuse but also dense, molecular gas. In diffuse gas, at lower densities a quiescent ion-neutral chemistry alone cannot account for the observed abundance of CH. Unlike the production of HF, for CH^+^ and CH, vortices forming in turbulent, diffuse gas may be the setting for an enhanced production path. However, CH remains a valuable tracer for molecular gas in environments reaching from diffuse clouds to sites of high-mass star formation.
- ID:
- ivo://CDS.VizieR/J/A+A/544/A26
- Title:
- CI Aql spectra during 2000 outburst
- Short Name:
- J/A+A/544/A26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High- and low-resolution optical spectra of CI Aql were obtained during the outburst in 2000. Multiple absorption components of HI and FeII lines were detected at the early decline stage. Their radial velocities were roughly -2500km/s, -2200km/s , -1700km/s, and -1400km/s, among which only the last components were likely still accelerating during the early decline stage. Prominent emission lines of [OIII] and [NII] appeared about one month after light maximum. The duration of the nebular stage, however, was only one month and a few weeks. The ejected gas shells seem to have started to shrink about 70 days after light maximum. The amount of interstellar extinction is estimated to be E(B-V)=0.92+/-0.15 from the equivalent widths of the diffuse interstellar absorption bands. The helium abundance in the ejecta is estimated to be N(He)=0.19+/-0.05 and the mass of the ejecta to be about 2x10^-6^M_{sun}_. This object has been classified as a U Sco type recurrent nova, but its spectral evolution during the outburst resembled those of T Pyx type recurrent novae. It is doubtful whether the peak of m_V_~9mag on 2000 May 5 was the true light maximum or an earlier brighter peak had been overlooked, because the spectral data suggest that the ejections of gas shells occurred prior to the discovery of the outburst on 2000 April 28.
