491 research outputs found
Abundances of Baade's Window Giants from Keck/HIRES Spectra: II. The Alpha- and Light Odd Elements
We report detailed chemical abundance analysis of 27 RGB stars towards the
Galactic bulge in Baade's Window for elements produced by massive stars: O, Na,
Mg, Al, Si, Ca and Ti. All of these elements are overabundant in the bulge
relative to the disk, especially Mg, indicating that the bulge is enhanced in
Type~II supernova ejecta and most likely formed more rapidly than the disk. We
attribute a rapid decline of [O/Fe] to metallicity-dependent yields of oxygen
in massive stars, perhaps connected to the Wolf-Reyet phenomenon. he explosive
nucleosynthesis alphas, Si, Ca and Ti, possess identical trends with [Fe/H],
consistent with their putative common origin. We note that different behaviors
of hydrostatic and explosive alpha elements can be seen in the stellar
abundances of stars in Local Group dwarf galaxies. We also attribute the
decline of Si,Ca and Ti relative to Mg, to metallicity- dependent yields for
the explosive alpha elements from Type~II supernovae. The starkly smaller
scatter of [/Fe] with [Fe/H] in the bulge, as compared to the halo, is
consistent with expected efficient mixing for the bulge. The metal-poor bulge
[/Fe] ratios are higher than ~80% of the halo. If the bulge formed from
halo gas, the event occured before ~80% of the present-day halo was formed. The
lack of overlap between the thick and thin disk composition with the bulge does
not support the idea that the bulge was built by a thickening of the disk
driven by the bar. The trend of [Al/Fe] is very sensitive to the chemical
evolution environment. A comparison of the bulge, disk and Sgr dSph galaxy
shows a range of ~0.7 dex in [Al/Fe] at a given [Fe/H], presumably due to a
range of Type~II/Type~Ia supernova ratios in these systems.Comment: 51 pages, 6 tables, 27 figures, submitte
A common coupling mechanism for A-type heme-copper oxidases from bacteria to mitochondria
Mitochondria metabolise almost all of the oxygen that we consume, reducing it to water by cytochrome c oxidase (CcO). CcO maximises energy capture into the protonmotive force by pumping protons across the mitochondrial inner membrane. Forty years after the H+/e- stoichiometry was established, a consensus has yet to be reached on the route taken by pumped protons to traverse CcO’s hydrophobic core and on whether bacterial and mitochondrial CcOs operate via the same coupling mechanism. To resolve this, we exploited the unique amenability to mitochondrial DNA mutagenesis of the yeast S. cerevisiae to introduce single point mutations in the hydrophilic pathways of CcO to test function. From ADP/O ratio measurements on preparations of intact mitochondria, we definitely established that the D-channel, and not the H-channel, is the proton pump of the yeast mitochondrial enzyme, supporting an identical coupling mechanism in all forms of the enzyme
Calibration of the Tip of the Red Giant Branch (TRGB)
The Tip of the Red Giant (TRGB) method provides one of the most accurate and
precise means of measuring the distances to nearby galaxies. Here we present a
VIJHK absolute calibration of the TRGB based on observations of TRGB stars in
the Large Magellanic Cloud (LMC),grounded on detached eclipsing binaries
(DEBs). This paper presents a more detailed description of the method first
presented in Freedman et al. (2019) for measuring corrections for the total
line-of-sight extinction and reddening to the LMC. In this method, we use a
differential comparison of the red giant population in the LMC, first with red
giants in the Local Group galaxy, IC 1613, and then with those in the Small
Magellanic Cloud. As a consistency check, we derive an independent calibration
of the TRGB sequence using the SMC alone, invoking its geometric distance also
calibrated by DEBs. An additional consistency check comes from near-infrared
observations of Galactic globular clusters covering a wide range of
metallicities. In all cases we find excellent agreement in the zero-point
calibration. We then examine the recent claims by Yuan et al. (2019),
demonstrating that, in the case of the SMC, they corrected for extinction alone
while neglecting the essential correction for reddening as well. In the case of
IC 1613, we show that their analysis contains an incorrect treatment of
(over-correction for) metallicity. Using our revised (and direct) measurement
of the LMC TRGB extinction, we find a value of Ho = 69.6 +/-0.8 (+/-1.1% stat)
+/- 1.7 (+/-2.4% sys) km/s/Mpc.Comment: 33 pages, 13 figures, accepted to the Astrophysical Journal February
4, 202
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Calibration of the Tip of the Red Giant Branch
The tip of the red giant branch (TRGB) method provides one of the most accurate and precise means of measuring the distances to nearby galaxies. Here we present a multi-wavelength, VIJHK absolute calibration of the TRGB based on observations of TRGB stars in the Large Magellanic Cloud (LMC), grounded on a geometric distance, determined by detached eclipsing binaries (DEBs). This paper presents a more detailed description of the method first presented by Freedman et al. for measuring corrections for the total line-of-sight extinction and reddening to the LMC. In this method, we use a differential comparison of the red giant population in the LMC, first with red giants in the Local Group galaxy IC 1613, and then with those in the Small Magellanic Cloud (SMC). As a consistency check, we derive an independent calibration of the TRGB sequence using the SMC alone, invoking its geometric distance also calibrated by DEBs. An additional consistency check comes from near-infrared observations of Galactic globular clusters covering a wide range of metallicities. In all cases we find excellent agreement in the zero-point calibration. We then examine the recent claims by Yuan et al., demonstrating that, in the case of the SMC, they corrected for extinction alone while neglecting the essential correction for reddening. In the case of IC 1613, we show that their analysis contains an incorrect treatment of (over-correction for) metallicity. Using our revised (and direct) measurement of the LMC TRGB extinction, we find a value of H0 = 69.6 ± 0.8 (±1.1% stat) ± 1.7 (±2.4% sys) km s−1 Mpc−1
The TYPHOON stellar population synthesis survey: I. The young stellar population of the Great Barred Spiral NGC 1365
We analyze TYPHOON long slit absorption line spectra of the starburst barred
spiral galaxy NGC 1365 obtained with the Progressive Integral Step Method
covering an area of 15 square kpc. Applying a population synthesis technique,
we determine the spatial distribution of ages and metallicity of the young and
old stellar population together with star formation rates, reddening,
extinction and the ratio R of extinction to reddening. We detect a clear
indication of inside-out growth of the stellar disk beyond 3 kpc characterized
by an outward increasing luminosity fraction of the young stellar population, a
decreasing average age and a history of mass growth, which was finished 2 Gyrs
later in the outermost disk. The metallicity of the young stellar population is
clearly super solar but decreases towards larger galactocentric radii with a
gradient of -0.02 dex/kpc. On the other hand, the metal content of the old
population does not show a gradient and stays constant at a level roughly 0.4
dex lower than that of the young population. In the center of NGC 1365 we find
a confined region where the metallicity of the young population drops
dramatically and becomes lower than that of the old population. We attribute
this to infall of metal poor gas and, additionally, to interrupted chemical
evolution where star formation is stopped by AGN and supernova feedback and
then after several Gyrs resumes with gas ejected by stellar winds from earlier
generations of stars. We provide a simple model calculation as support for the
latter
Standard Galactic Field RR Lyrae. I. Optical to Mid-infrared Phased Photometry
We present a multi-wavelength compilation of new and previously published photometry for 55 Galactic field RR Lyrae variables. Individual studies, spanning a time baseline of up to 30 years, are self-consistently phased to produce light curves in 10 photometric bands covering the wavelength range from 0.4 to 4.5 microns. Data smoothing via the GLOESS technique is described and applied to generate high-fidelity light curves, from which mean magnitudes, amplitudes, rise times, and times of minimum and maximum light are derived. 60,000 observations were acquired using the new robotic Three-hundred MilliMeter Telescope (TMMT), which was first deployed at the Carnegie Observatories in Pasadena, CA, and is now permanently installed and operating at Las Campanas Observatory in Chile. We provide a full description of the TMMT hardware, software, and data reduction pipeline. Archival photometry contributed approximately 31,000 observations. Photometric data are given in the standard Johnson UBV, Kron–Cousins , 2MASS JHK, and Spitzer [3.6] and [4.5] bandpasses
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