65 research outputs found
Living Together and Voting Together: The Impact of Congressional Boardinghouse Networks on Voting Patterns, 1825-1841
In the early part of the XIX century, American politics had a local flavor. Weak parties proved incapable of articulating national political identities and Congress operated in large part reactively to the given issues of the day. Yet despite the political fragmentation that characterized this period, by 1830 the contours of a national political stage had emerged (Formisano 1983). In this paper, we focus on the role of shared Congressional living arrangements as a cause of this ideological consolidation. We show that it was only when Congressmen from the South (North) lived in boardinghouses with other Congressmen from the South (North) that they realized their commonality of interests. Further, we use a particular aspect of our data—Congressmen that moved between boardinghouses at the end of the first session—to separate the impact of selection from that of political influence. Rather than choosing to live together on the basis of common regional interests, Congressmen recognized these interests because they lived together
LTE or non-LTE, that is the question
Strontium has proven itself to be one of the most important neutron-capture
elements in the study of metal-poor stars. Thanks to the strong absorption
lines of Sr, they can be detected even in the most metal-poor stars and also in
low-resolution spectra. However, we still cannot explain the large star-to-star
abundance scatter we derive for metal-poor stars. Here we contrast Galactic
chemical evolution (GCE) with improved abundances for SrI+II including updated
atomic data, to evaluate possible explanations for the large star-to-star
scatter at low metallicities. We derive abundances under both local
thermodynamic equilibrium (LTE) and non-LTE (NLTE) for stars spanning a large
interval of stellar parameters. Gravities and metallicities are also determined
in NLTE. We confirm that the ionisation equilibrium between SrI and SrII is
satisfied under NLTE but not LTE, where the difference between SrI and SrII is
on average ~0.3dex. We show that the NLTE corrections are of increasing
importance as the metallicity decreases. For the stars with [Fe/H]>-3 the SrI
NLTE correction is ~0.35/0.55dex in dwarfs/giants, while the Sr II NLTE
correction is +/-0.05dex. On the basis of the large NLTE corrections, SrI
should not be applied as a chemical tracer under LTE, while it is a good tracer
under NLTE. SrII is a good tracer under both LTE and NLTE (down to [Fe/H]\sim
-3), and LTE is a safe assumption for this majority species. However, the Sr
abundance from SrII lines is dependent on an accurate surface gravity
determination, which can be obtained from NLTE spectroscopy of Fe lines or from
parallax measurements. We could not explain the star-to-star scatter (which
remains under both LTE and NLTE) by the use of the GCE model, since the Sr
yields to date are too uncertain to draw firm conclusions. At least two
production sites seem necessary in order to account for this large scatter
(abridged).Comment: 14 pages, 12 figures and one online table (accepted by A&A
Red supergiants as cosmic abundance probes: The first direct metallicity determination of NGC 4038 in the antennae.
We present a direct determination of the stellar metallicity in the close pair galaxy NGC 4038 (D= 20 Mpc) based on the quantitative analysis of moderate resolution KMOS/VLT spectra of three super star clusters (SSCs). The method adopted in our analysis has been developed and optimised to measure accurate metallicities from atomic lines in the J-band of single red supergiant (RSG) or RSG-dominated star clusters. Hence, our metallicity measurements are not a_ected by the biases and poorly understood systematics inherent to strong line H II methods which are routinely applied to massive data sets of galaxies. We _nd [Z]= +0.07 _ 0.03 and compare our measurements to H II strong line calibrations. Our abundances and literature data suggest the presence of a at metallicity gradient, which can be explained as redistribution of metal-rich gas following the strong interaction
RED SUPERGIANTS AS COSMIC ABUNDANCE PROBES: THE MAGELLANIC CLOUDS
Red Supergiants (RSGs) are cool (∼ 4000K), highly luminous stars (L ∼ 105L⊙), and are among the
brightest near-infrared (NIR) sources in star-forming galaxies. This makes them powerful probes of
the properties of their host galaxies, such as kinematics and chemical abundances. We have developed
a technique whereby metallicities of RSGs may be extracted from a narrow spectral window around
1μm from only moderate resolution data. The method is therefore extremely efficient, allowing stars
at large distances to be studied, and so has tremendous potential for extragalactic abundance work.
Here, we present an abundance study of the Large and Small Magellanic Clouds (LMC and SMC
respectively) using samples of 9-10 RSGs in each. We find average abundances for the two galaxies of
[Z]LMC = −0.37±0.14 and [Z]SMC = −0.53±0.16 (with respect to a Solar metallicity of Z⊙=0.012).
These values are consistent with other studies of young stars in these galaxies, and though our result for
the SMC may appear high it is consistent with recent studies of hot stars which find 0.5-0.8dex below
Solar. Our best-fit temperatures are on the whole consistent with those from fits to the optical-infrared spectral energy distributions, which is remarkable considering the narrow spectral range being studied.
Combined with our recent study of RSGs in the Galactic cluster Per OB1, these results indicate that
this technique performs well over a range of metallicities, paving the way for forthcoming studies of
more distant galaxies beyond the Local Group
Red Supergiants as Cosmic Abundance Probes: massive star clusters in M83, and the mass-metallicity relation of nearby galaxies
We present an abundance analysis of seven super-star clusters in the disk of M83. The near-infrared spectra of these clusters are dominated by Red Supergiants, and the spectral similarity in the J-band of such stars at uniform metallicity means that the integrated light from the clusters may be analysed using the same tools as those applied to single stars. Using data from VLT/KMOS we estimate metallicities for each cluster in the sample. We find that the abundance gradient in the inner regions of M83 is flat, with a central metallicity of [Z] = 0.210.11 relative to a Solar value of =0.014, which is in excellent agreement with the results from an analysis of luminous hot stars in the same regions. Compiling this latest study with our other recent work, we construct a mass-metallicity relation for nearby galaxies based entirely on the analysis of RSGs. We find excellent agreement with the other stellar-based technique, that of blue supergiants, as well as with temperature-sensitive (`auroral' or `direct') \hii-region studies. Of all the HII-region strong-line calibrations, those which are empirically calibrated to direct-method studies (N2 and O3N2) provide the most consistent results
Physical properties of the first spectroscopically confirmed red supergiant stars in the Sculptor Group galaxy NGC 55
We present K-band Multi-Object Spectrograph (KMOS) observations of 18 red supergiant (RSG) stars in the Sculptor Group galaxy NGC 55. Radial velocities are calculated and are shown to be in good agreement with previous estimates, confirming the supergiant nature of the targets and providing the first spectroscopically confirmed RSGs in NGC 55. Stellar parameters are estimated for 14 targets using the J-band analysis technique, making use of state-of-the-art stellar model atmospheres. The metallicities estimated confirm the low-metallicity nature of NGC 55, in good agreement with previous studies. This study provides an independent estimate of the metallicity gradient of NGC 55, in excellent agreement with recent results published using hot massive stars. In addition, we calculate luminosities of our targets and compare their distribution of effective temperatures and luminosities to that of other RSGs, in different environments, estimated using the same technique
A New Method for Measuring Metallicities of Young Super Star Clusters
We demonstrate how the metallicities of young super star clusters (SSC) can be measured using novel spectroscopic techniques in the J-band. The near-infrared flux of SSCs older than ~6 Myr is dominated by tens to hundreds of red supergiant stars. Our technique is designed to harness the integrated light of that population and produces accurate metallicities for new observations in galaxies above (M83) and below (NGC 6946) solar metallicity. In M83 we find [Z] = +0.28 ± 0.14 dex using a moderate resolution (R ~ 3500) J-band spectrum and in NGC 6496 we report [Z] = -0.32 ± 0.20 dex from a low resolution spectrum of R ~ 1800. Recently commissioned low resolution multiplexed spectrographs on the Very Large Telescope (KMOS) and Keck (MOSFIRE) will allow accurate measurements of SSC metallicities across the disks of star-forming galaxies up to distances of 70 Mpc with single night observation campaigns using the method presented in this paper
Stellar Astrophysics and Exoplanet Science with the Maunakea Spectroscopic Explorer (MSE)
The Maunakea Spectroscopic Explorer (MSE) is a planned 11.25-m aperture
facility with a 1.5 square degree field of view that will be fully dedicated to
multi-object spectroscopy. A rebirth of the 3.6m Canada-France-Hawaii Telescope
on Maunakea, MSE will use 4332 fibers operating at three different resolving
powers (R ~ 2500, 6000, 40000) across a wavelength range of 0.36-1.8mum, with
dynamical fiber positioning that allows fibers to match the exposure times of
individual objects. MSE will enable spectroscopic surveys with unprecedented
scale and sensitivity by collecting millions of spectra per year down to
limiting magnitudes of g ~ 20-24 mag, with a nominal velocity precision of ~100
m/s in high-resolution mode. This white paper describes science cases for
stellar astrophysics and exoplanet science using MSE, including the discovery
and atmospheric characterization of exoplanets and substellar objects, stellar
physics with star clusters, asteroseismology of solar-like oscillators and
opacity-driven pulsators, studies of stellar rotation, activity, and
multiplicity, as well as the chemical characterization of AGB and extremely
metal-poor stars.Comment: 31 pages, 11 figures; To appear as a chapter for the Detailed Science
Case of the Maunakea Spectroscopic Explore
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