- ID:
- ivo://CDS.VizieR/J/A+A/635/A150
- Title:
- CasA, CygA, TauA, VirA 30MHz & 77MHz models
- Short Name:
- J/A+A/635/A150
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The four persistent radio sources in the northern sky with the highest flux density at metre wavelengths are Cassiopeia A, Cygnus A, Taurus A, and Virgo A; collectively they are called the A-team. Their flux densities at ultra-low frequencies (<100MHz) can reach several thousands of janskys, and they often contaminate observations of the low-frequency sky by interfering with image processing. Furthermore, these sources are foreground objects for all-sky observations hampering the study of faint signals, such as the cosmological 21cm line from the epoch of reionisation. We aim to produce robust models for the surface brightness emission as a function of frequency for the A-team sources at ultra-low frequencies. These models are needed for the calibration and imaging of wide-area surveys of the sky with low-frequency interferometers. This requires obtaining images at an angular resolution better than 1500 with a high dynamic range and good image fidelity. We observed the A-team with the Low Frequency Array (LOFAR) at frequencies between 30MHz and 77MHz using the Low Band Antenna (LBA) system. We reduced the datasets and obtained an image for each A-team source. The paper presents the best models to date for the sources Cassiopeia A, Cygnus A, Taurus A, and Virgo A between 30MHz and 77MHz. We were able to obtain the aimed resolution and dynamic range in all cases. Owing to its compactness and complexity, observations with the long baselines of the International LOFAR Telescope will be required to improve the source model for Cygnus A further.
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- ID:
- ivo://CDS.VizieR/J/ApJ/613/343
- Title:
- Cas A knot and filament proper motions
- Short Name:
- J/ApJ/613/343
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-resolution X-ray proper-motion measurements of Cassiopeia A using Chandra X-Ray Observatory observations from 2000 and 2002. We separate the emission into four spectrally distinct classes: Si-dominated, Fe-dominated, low-energy-enhanced, and continuum-dominated. These classes also represent distinct spatial and kinematic components.
- ID:
- ivo://CDS.VizieR/J/A+A/612/A110
- Title:
- Cas A LOFAR and VLA images
- Short Name:
- J/A+A/612/A110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Cassiopeia A is one of the best-studied supernova remnants. Its bright radio and X-ray emission is due to shocked ejecta. Cas A is rather unique in that the unshocked ejecta can also be studied: through emission in the infrared, the radio-active decay of ^44^Ti, and the low-frequency free-free absorption caused by cold ionised gas, which is the topic of this paper. Free-free absorption processes are acted by the mass, geometry, temperature, and ionisation conditions in the absorbing gas. Observations at the lowest radio frequencies can constrain a combination of these properties. We used Low Frequency Array (LOFAR) Low Band Antenna observations at 30-77MHz and Very Large Array (VLA) L-band observations at 1-2GHz to fit for internal absorption as parametrised by the emission measure. We simultaneously fit multiple UV-matched images with a common resolution of 17" (this corresponds to 0.25pc for a source at the distance of Cas A). The ample frequency coverage allows us separate the relative contributions from the absorbing gas, the unabsorbed front of the shell, and the absorbed back of the shell to the emission spectrum. We explored the effects that a temperature lower than the ~100-500K proposed from infrared observations and a high degree of clumping can have on the derived physical properties of the unshocked material, such as its mass and density. We also compiled integrated radio flux density measurements, fit for the absorption processes that occur in the radio band, and considered their ect on the secular decline of the source. We find a mass in the unshocked ejecta of M=2.95+/-0.48M_{sun}_ for an assumed gas temperature of T=100K. This estimate is reduced for colder gas temperatures and, most significantly, if the ejecta are clumped.We measure the reverse shock to have a radius of 114+/-6" and be centred at 23:23:26, +58:48:54 (J2000).We also find that a decrease in the amount of mass in the unshocked ejecta (as more and more material meets the reverse shock and heats up) cannot account for the observed low-frequency behaviour of the secular decline rate. To reconcile our low-frequency absorption measurements with models that reproduce much of the observed behaviour in Cas A and predict little mass in the unshocked ejecta, the ejecta need to be very clumped or the temperature in the cold gas needs to be low (~10K). Both of these options are plausible and can together contribute to the high absorption value that we find.
- ID:
- ivo://CDS.VizieR/J/ApJ/456/234
- Title:
- Cas A radio knots spectral indices
- Short Name:
- J/ApJ/456/234
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have determined the synchrotron spectral indices of 304 compact radio knots in the supernova remnant Cassiopeia A. A comparison of these data with the dynamical and brightness properties of these knots tabulated by Anderson & Rudnick (Cat. <J/ApJ/441/307>) indicates that spectral index shows a significant correlation with projected radius from the center of the remnant. Spectrally flat knots reside in a shell coincident with the bright radio ring, while steeper knots occupy a shell coincident with the diffuse radio plateau surrounding the ring. To a lesser extent, we find spectral index to be correlated also with the radio brightness of the knot, in the sense that brighter knots tend to have steeper spectra. No significant correlation is found between spectral index and knot deceleration or rate of brightness change. As the synchrotron spectral index traces the distribution of energy among relativistic particle populations, we use these results to study the nature of particle acceleration mechanisms active in Cas A. Given the dual shell nature of the spectral index distribution in Cas A and the lack of strong correlation between spectral index and dynamical properties of the knots, we conclude that radio-bright compact features are not sites of currently active particle acceleration in Cas A. This conclusion is in agreement with models of supersonic gaseous bullets constructed by Jones, Kang, & Tregillis (1994ApJ...432..194J). In these models, the marked synchrotron brightening which accompanies bullet deceleration is due primarily to preexisting relativistic particles radiating in rapidly amplifying shear-layer magnetic fields, rather than a large infusion of new relativistic particles accelerated in situ. Spectral variations between compact features in Cas A are more likely to reflect modulations in the background particle energy spectra within the remnant, perhaps instilled by temperature variations in the underlying thermal material. This interpretation requires that the diffuse synchrotron emission show the same spectral variations as seen in compact features; preliminary indications suggest that this is the case.
- ID:
- ivo://CDS.VizieR/J/A+A/657/A87
- Title:
- CASCADES I. Sample definition and first results
- Short Name:
- J/A+A/657/A87
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Following the first discovery of a planet orbiting a giant star in 2002, we started the CORALIE radial-velocity search for companions around evolved stars (CASCADES). We present the observations of three stars conducted at the 1.2m Leonard Euler Swiss telescope at La Silla Observatory, Chile, using the CORALIE spectrograph. We aim to detect planetary companions to intermediate-mass G- and K- type evolved stars and perform a statistical analysis of this population. We searched for new planetary systems around the stars HD22532 (TIC200851704), HD64121 (TIC264770836), and HD69123 (TIC146264536). We have followed a volume-limited sample of 641 red giants since 2006 to obtain high-precision radial-velocity measurements. We used the Data & Analysis Center for Exoplanets (DACE) platform to perform a radial-velocity analysis to search for periodic signals in the line profile and activity indices, to distinguish between planetary-induced radial-velocity variations and stellar photospheric jitter, and to search for significant signals in the radial-velocity time series to fit a corresponding Keplerian model. In this paper, we present the survey in detail, and we report on the discovery of the first three planets of the sample around the giant stars HD22532, HD64121, and HD69123.
- ID:
- ivo://CDS.VizieR/J/AJ/109/2376
- Title:
- Case blue/emission-line galaxies
- Short Name:
- J/AJ/109/2376
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present CCD imaging and spectroscopic data for 176 blue and/or emission-line galaxies from Lists I and II of the Case Northern Sky Survey. Our sample consists of all Case galaxies which lie in the region which overlaps the original Slice of the Universe survey. We use the observational data to investigate the physical properties of the galaxies selected by the surveys to compare with various parameters published in the survey lists, and to investigate the selection characteristics and completeness limit of the survey. The majority of the Case galaxies are energized by regions of active star formation; only 5% of the sample are Seyfert galaxies. The dual selection techniques used (both UV-excess and emission lines) allow the survey to detect star-forming galaxies with a wide range of properties and evolutionary states. In particular, the Case survey selects galaxies with lower levels of activity than most previous surveys. The survey also includes a larger fraction of intermediate and low-luminosity galaxies than would be present in a purely magnitude-limited sample. Although galaxies as faint as m_B_=19 are present in the sample, the completeness limit of the UV-excess selected portion of the survey is closer to m_B_=16. The luminosity function of the Case galaxies is derived and compared with that of the "normal" field galaxies in the same volume of space. The shape of the Case luminosity function is similar to that for the field sample. A surprising result is that 31% of the field galaxy population can be accounted for by galaxies of the type selected in the Case survey.
- ID:
- ivo://CDS.VizieR/J/ApJS/66/309
- Title:
- Case low-dispersion Survey VI
- Short Name:
- J/ApJS/66/309
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Positions, estimated magnitudes, and finding charts (when needed) are provided for 183 A-F stars (including both Population I and horizontal-branch stars) contained within the region 12h00m <R.A> <13h00m and +29.0 <decl. <+34.0. These stars, whose blue magnitudes range from 5.5 to 17.5, were identified on low-dispersion, objective-prism plates taken with the Burrell Schmidt telescope.
- ID:
- ivo://CDS.VizieR/J/ApJS/66/387
- Title:
- Case low-dispersion Survey VII.
- Short Name:
- J/ApJS/66/387
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observational data on 132 faint (R magnitude = 9-17) red stars with carbon-star or late M-type spectra are presented in tables and briefly characterized. The data were collected in a survey of a 1000-sq deg region at high northern Galactic latitude (right ascension 8h15 to 17h30 and declination +29 to +38 deg) on low-dispersion 330-535-nm objective-prism plates obtained with the 61/91-cm Burrell Schmidt telescope at Kitt Peak Observatory.
- ID:
- ivo://CDS.VizieR/J/ApJS/71/549
- Title:
- Case low-dispersion Survey X.
- Short Name:
- J/ApJS/71/549
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Position, estimated magnitudes, and finding charts are provided for 540 A-F stars in the region 8h00m <R.A< 11h10m and +29.0 <Decl.<+43.0 (1950). The Galactic latitudes lie within the range +27 and +68. The A-F stars, with blue magnitudes between 14 and 17, were identified on low-dispersion objective-prism plates taken with the Burell Schmidt telescope. A large fraction of these A-F stars are expected to belong to Population II.
- ID:
- ivo://CDS.VizieR/J/AJ/145/43
- Title:
- CASE. V. Three eclipsing binaries in M4
- Short Name:
- J/AJ/145/43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use photometric and spectroscopic observations of the eclipsing binaries V65, V66, and V69 in the field of the globular cluster M4 to derive masses, radii, and luminosities of their components. The orbital periods of these systems are 2.29, 8.11, and 48.19days, respectively. The measured masses of the primary and secondary components (M_p_ and M_s_) are 0.8035+/-0.0086 and 0.6050+/-0.0044M_{sun}_ for V65, 0.7842+/-0.0045 and 0.7443+/-0.0042M_{sun}_ for V66, and 0.7665+/-0.0053 and 0.7278+/-0/0048M_{sun}_ for V69. The measured radii (R_p_ and R_s_) are 1.147+/-0.010 and 0.6110 +/- 0.0092R_{sun}_ for V66, 0.9347+/-0.0048 and 0.8298+/-0.0053R_{sun}_ for V66, and 0.8655+/-0.0097 and 0.8074+/-0.0080R_{sun}_ for V69. The orbits of V65 and V66 are circular, whereas that of V69 has an eccentricity of 0.38. Based on systemic velocities and relative proper motions, we show that all three systems are members of the cluster. We find that the distance to M4 is 1.82+/-0.04kpc-in good agreement with recent estimates based on entirely different methods. We compare the absolute parameters of V66 and V69 with two sets of theoretical isochrones in mass-radius and mass-luminosity diagrams, and for assumed [Fe/H]=-1.20, [{alpha}/Fe]=0.4, and Y=0.25 we find the most probable age of M4 to be between 11.2 and 11.3Gyr. Color-magnitude diagram (CMD) fitting with the same parameters yields an age close to, or slightly in excess of, 12Gyr. However, considering the sources of uncertainty involved in CMD fitting, these two methods of age determination are not discrepant. Age and distance determinations can be further improved when infrared eclipse photometry is obtained.
