- ID:
- ivo://CDS.VizieR/J/MNRAS/469/1186
- Title:
- Emission-line strengths for 129 galaxies
- Short Name:
- J/MNRAS/469/1186
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We propose a method to substantially increase the flexibility and power of template fitting-based photometric redshifts by transforming a large number of galaxy spectral templates into a corresponding collection of 'fuzzy archetypes' using a suitable set of perturbative priors designed to account for empirical variation in dust attenuation and emission-line strengths. To bypass widely separated degeneracies in parameter space (e.g. the redshift-reddening degeneracy), we train self-organizing maps (SOMs) on large 'model catalogues' generated from Monte Carlo sampling of our fuzzy archetypes to cluster the predicted observables in a topologically smooth fashion. Subsequent sampling over the SOM then allows full reconstruction of the relevant probability distribution functions (PDFs). This combined approach enables the multimodal exploration of known variation among galaxy spectral energy distributions with minimal modelling assumptions. We demonstrate the power of this approach to recover full redshift PDFs using discrete Markov chain Monte Carlo sampling methods combined with SOMs constructed from Large Synoptic Survey Telescope ugrizY and Euclid YJH mock photometry.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/759/141
- Title:
- Emission measures in solar active regions
- Short Name:
- J/ApJ/759/141
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The recent analysis of observations taken with the EUV Imaging Spectrometer and X-Ray Telescope instruments on Hinode suggests that well-constrained measurements of the temperature distribution in solar active regions can finally be made. Such measurements are critical for constraining theories of coronal heating. Past analysis, however, has suffered from limited sample sizes and large uncertainties at temperatures between 5 and 10MK. Here we present a systematic study of the differential emission measure distribution in 15 active region cores. We focus on measurements in the "inter-moss" region, that is, the region between the loop footpoints, where the observations are easier to interpret. To reduce the uncertainties at the highest temperatures we present a new method for isolating the Fe XVIII emission in the AIA/SDO 94{AA} channel. The resulting differential emission measure distributions confirm our previous analysis showing that the temperature distribution in an active region core is often strongly peaked near 4MK. We characterize the properties of the emission distribution as a function of the total unsigned magnetic flux. We find that the amount of high-temperature emission in the active region core is correlated with the total unsigned magnetic flux, while the emission at lower temperatures, in contrast, is inversely related. These results provide compelling evidence that high-temperature active region emission is often close to equilibrium, although weaker active regions may be dominated by evolving million degree loops in the core.
- ID:
- ivo://CDS.VizieR/J/ApJ/880/127
- Title:
- EMPIRE: IRAM 30m dense gas survey
- Short Name:
- J/ApJ/880/127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present EMPIRE, an IRAM 30m large program that mapped {lambda}=3-4mm dense gas tracers at ~1-2kpc resolution across the whole star-forming disk of nine nearby massive spiral galaxies. We describe the EMPIRE observing and reduction strategies and show new whole-galaxy maps of HCN(1-0), HCO^+^(1-0), HNC(1-0), and CO(1-0). We explore how the HCN-to-CO and IR-to-HCN ratios, observational proxies for the dense gas fraction and dense gas star formation efficiency, depend on host galaxy and local environment. We find that the fraction of dense gas correlates with stellar surface density, gas surface density, molecular-to-atomic gas ratio, and dynamical equilibrium pressure. In EMPIRE, the star formation rate per unit dense gas is anticorrelated with these same environmental parameters. Thus, although dense gas appears abundant in the central regions of many spiral galaxies, this gas appears relatively inefficient at forming stars. These results qualitatively agree with previous work on nearby galaxies and the Milky Way's Central Molecular Zone. To first order, EMPIRE demonstrates that the conditions in a galaxy disk set the gas density distribution and that the dense gas traced by HCN shows an environment-dependent relation to star formation. However, our results also show significant (+/-0.2dex) galaxy-to-galaxy variations. We suggest that gas structure below the scale of our observations and dynamical effects likely also play an important role.
- ID:
- ivo://CDS.VizieR/J/ApJ/804/64
- Title:
- Empirical and model parameters of 183 M dwarfs
- Short Name:
- J/ApJ/804/64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Precise and accurate parameters for late-type (late K and M) dwarf stars are important for characterization of any orbiting planets, but such determinations have been hampered by these stars' complex spectra and dissimilarity to the Sun. We exploit an empirically calibrated method to estimate spectroscopic effective temperature (T_eff_) and the Stefan-Boltzmann law to determine radii of 183 nearby K7-M7 single stars with a precision of 2%-5%. Our improved stellar parameters enable us to develop model-independent relations between T_eff_ or absolute magnitude and radius, as well as between color and T_eff_. The derived T_eff_-radius relation depends strongly on [Fe/H], as predicted by theory. The relation between absolute K_S_magnitude and radius can predict radii accurate to ~=3%. We derive bolometric corrections to the VR_C_I_C_grizJHK_S_ and Gaia passbands as a function of color, accurate to 1%-3%. We confront the reliability of predictions from Dartmouth stellar evolution models using a Markov chain Monte Carlo to find the values of unobservable model parameters (mass, age) that best reproduce the observed effective temperature and bolometric flux while satisfying constraints on distance and metallicity as Bayesian priors. With the inferred masses we derive a semi-empirical mass-absolute magnitude relation with a scatter of 2% in mass. The best-agreement models overpredict stellar T_eff_ values by an average of 2.2% and underpredict stellar radii by 4.6%, similar to differences with values from low-mass eclipsing binaries. These differences are not correlated with metallicity, mass, or indicators of activity, suggesting issues with the underlying model assumptions, e.g., opacities or convective mixing length.
- ID:
- ivo://CDS.VizieR/J/A+AS/139/29
- Title:
- Empirical calibration of the 4000 A break
- Short Name:
- J/A+AS/139/29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Empirical fitting functions, describing the behaviour of the {lambda}4000{AA} break in terms of effective temperature, metallicity and surface gravity, are presented. For this purpose, the break has been measured in 392 stars from the Lick/IDS Library. We have followed a very detailed error treatment in the reduction and fitting procedures, allowing for a reliable estimation of the break uncertainties. This calibration can be easily incorporated into stellar population models to provide accurate predictions of the break amplitude for, relatively old, composite systems. Table 1 lists the star sample, together with spectral types, adopted atmospheric parameters, break measurements, including errors, and residuals from the fitting functions.
- ID:
- ivo://CDS.VizieR/J/MNRAS/326/959
- Title:
- Empirical calibration of the near-IR Ca triplet
- Short Name:
- J/MNRAS/326/959
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- File table contains details of the new near-IR stellar library observed to calibrate the Ca II triplet. It includes the indices CaT*, CaT and PaT measured over the final spectra as well as their corresponding errors. The Henry Draper Catalogue number, other names (mainly HR and BD numbers), coordinates, spectral type, luminosity class, apparent magnitude and atmospheric parameters (as derived in Paper II; Cenarro et al., 2001MNRAS.326..981C) are also given.
- ID:
- ivo://CDS.VizieR/J/ApJ/813/12
- Title:
- Empirical methane (CH_4_) line list
- Short Name:
- J/ApJ/813/12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Hot methane is found in many "cool" sub-stellar astronomical sources including brown dwarfs and exoplanets, as well as in combustion environments on Earth. We report on the first high-resolution laboratory absorption spectra of hot methane at temperatures up to 1200K. Our observations are compared to the latest theoretical spectral predictions and recent brown dwarf spectra. The expectation that millions of weak absorption lines combine to form a continuum, not seen at room temperature, is confirmed. Our high-resolution transmittance spectra account for both the emission and absorption of methane at elevated temperatures. From these spectra, we obtain an empirical line list and continuum that is able to account for the absorption of methane in high temperature environments at both high and low resolution. Great advances have recently been made in the theoretical prediction of hot methane, and our experimental measurements highlight the progress made and the problems that still remain.
- ID:
- ivo://CDS.VizieR/J/A+A/371/579
- Title:
- Empirical relations for cluster RR Lyrae
- Short Name:
- J/A+A/371/579
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our former study on the empirical relations between the Fourier parameters of the light curves of the fundamental mode RR Lyrae stars and their basic stellar parameters has been extended to considerably larger data sets. The most significant contribution to the absolute magnitude M_V_ comes from the period P and from the first Fourier amplitude A_1_, but there are statistically significant contributions also from additional higher order components, most importantly from A_3_ and in a lesser degree from the Fourier phase phi_51_. When different colors are combined in reddening-free quantities, we obtain basically period-luminosity-color relations. From the standard deviations of the various regressions, an upper limit can be obtained on the overall inhomogeneity of the reddening in the individual clusters. This yields {sigma}_E(B-V)_<0.012mag, which also implies an average minimum observational error of {sigma}_V_>0.018mag.
- ID:
- ivo://CDS.VizieR/J/ApJ/774/6
- Title:
- Empirical scaling laws for shell dynamos
- Short Name:
- J/ApJ/774/6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Numerical dynamo models always employ parameter values that differ by orders of magnitude from the values expected in natural objects. However, such models have been successful in qualitatively reproducing properties of planetary and stellar dynamos. This qualitative agreement fuels the idea that both numerical models and astrophysical objects may operate in the same asymptotic regime of dynamics. This can be tested by exploring the scaling behavior of the models. For convection-driven incompressible spherical shell dynamos with constant material properties, scaling laws had been established previously that relate flow velocity and magnetic field strength to the available power. Here we analyze 273 direct numerical simulations using the anelastic approximation, involving also cases with radius-dependent magnetic, thermal, and viscous diffusivities. These better represent conditions in gas giant planets and low-mass stars compared to Boussinesq models. Our study provides strong support for the hypothesis that both mean velocity and mean magnetic field strength scale as a function of the power generated by buoyancy forces in the same way for a wide range of conditions.
- ID:
- ivo://CDS.VizieR/J/PASP/108/313
- Title:
- Empirical stellar flux scales
- Short Name:
- J/PASP/108/313
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Several studies have appeared in the literature describing methods for deriving stellar continuum fluxes as simple functions of Johnson color indices. In previous papers, we have used similar relations to derive Ca II H & K line core fluxes for dwarf stars on Lowell Observatory's Solar-Stellar Spectrograph (SSS) program. Our desire is to present our data, and complementary data from the Mt. Wilson and National Solar Observatory stellar and solar programs, in terms of physical fluxes. However, our existing relations break down for mid-K and later stars and for giant stars, which form an important element of our target list. In this work I have used a broader range of spectrophotometry and angular diameters than in our previous work to derive empirical flux scales for spectral types A to early M, luminosity classes I to V, and for four color indices, Johnson B-V, V-R, R-I, and Stromgren b-y. In this paper I describe the methods I used and present the derived flux scales. I compare the results with those from earlier studies and present examples of the use of the flux scales. The data and results are available on the World Wide Web home page. Access <http://www.lowell.edu>, select "Lowell staff", and select the author's home page.