193 research outputs found
Double-Mode RR Lyrae Variables in the Globular Cluster M3
We present new B-band CCD photometry for five double-mode RR Lyrae (RRd) variables (V68, V79, V87, V99, and V166) in the globular cluster M3. The pulsational behavior of the RRd variables is described. V68 and V87 have been known as RRd variables since 1982, V79 was recently discovered as an RRd (Clement et al.), and our data have identified V99 and V166 as RRd variables (Corwin et al.). Earlier studies of V79 and V166 do not show double-mode behavior, which indicates that these stars have only recently become RRd stars. V166 changed its dominant pulsation mode from fundamental to first overtone in the interval 1992 to 1993. The candidate double-mode variables V28 and V126 do not exhibit clear RRd behavior in the 1992â1993 data
Discovery of a Variable Star Population in NGC 2808
We have applied the image subtraction method to images of the peculiar,
bimodal-horizontal branch globular cluster NGC 2808, taken over a total of six
nights over a range of five months. As a result, we have found, for the first
time, a sizeable population of variable stars in the crowded inner regions of
the cluster, thus raising the known RR Lyrae population in the cluster to a
total of 18 stars. In addition, an eclipsing binary and two other variables
with periods longer than 1 day were also found. Periods, positions and
(differential) light curves are provided for all the detected variables. The
Oosterhoff classification of NGC 2808, which has recently been associated with
a previously unknown dwarf galaxy in Canis Major, is briefly discussed.Comment: 8 pages, 4 figures. A&A, in pres
Image-Subtraction Photometry of Variable Stars in the Globular Clusters NGC 6388 and NGC 6441
We have applied Alard's image subtraction method (ISIS v2.1) to the
observations of the globular clusters NGC 6388 and NGC 6441 previously analyzed
using standard photometric techniques (DAOPHOT, ALLFRAME). In this reanalysis
of observations obtained at CTIO, besides recovering the variables previously
detected on the basis of our ground-based images, we have also been able to
recover most of the RR Lyrae variables previously detected only in the analysis
of Hubble Space Telescope WFPC2 observations of the inner region of NGC6441. In
addition, we report five possible new variables not found in the analysis of
the HST observations of NGC 6441. This dramatically illustrates the
capabilities of image subtraction techniques applied to ground-based data to
recover variables in extremely crowded fields. We have also detected twelve new
variables and six possible variables in NGC 6388 not found in our previous
ground-based studies. The revised mean period for RRab stars in NGC 6388 is
0.676 day, while the mean period of RRab stars in NGC 6441 is unchanged at
0.759 day. These values are among the largest known for any galactic globular
cluster. Additional probable type II Cepheids were identified in NGC 6388,
confirming its status as a metal-rich globular cluster rich in Cepheids.Comment: 11 pages, 10 figures. AJ, in pres
The Globular Cluster M15. I. Identification, Discovery, and Period Determination of Variable Stars
We present new CCD photometry for variables in the globular cluster
M15. Our photometry was obtained using both the image subtraction package ISIS
and DAOPHOT/ALLFRAME. The data were acquired in 2001 on two observing runs on
11 observing nights using the 2-m telescope of the Bulgarian National
Astronomical Observatory ``Rozhen'' with a Photometrics CCD camera. For 40
previously known variables, we present a period for the first time, and
improved periods were obtained for many previously known variables. Fourteen
new variables are reported. We present updated Bailey diagrams for the cluster
and discuss its Oosterhoff classification. Although many of M15's RRab
pulsators fall at an intermediate locus between Oosterhoff types I and II in
the Bailey diagram, we argue that M15 is indeed a bona-fide Oosterhoff type IIComment: 48 pages, 7 figures, 3 table
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Undergraduates Phenotyping Arabidopsis Knockouts in a Course-Based Undergraduate Research Experience: Exploring Plant Fitness and Vigor Using Quantitative Phenotyping Methods â
We present a curriculum description, an initial student outcome investigation, and sample scientific results for a representative Course-Based Undergraduate Research Experience (CURE) that is part of the “Undergraduates Phenotyping Arabidopsis Knockouts” (unPAK) network. CUREs in the unPAK network characterize quantitative phenotypes of the model plant Arabidopsis from across environments to uncover connections between genotype and phenotype. Students in unPAK CUREs grow plants in a replicated block design and make quantitative measurements throughout the semester. This CURE enables students to answer plant science questions that draw from fields such as environmental science, genetics, ecology, and evolution. Findings indicate that this experience provides students with opportunities to make relevant scientific discoveries. Eighty percent of student datasets produced from the CURE met criteria for inclusion in the project database, indicative of student learning in data collection and analysis of quantitative plant traits. Student datasets uncovered novel effects of mutation on plant form. In addition, students’ science self-efficacy increased as a result of course participation, and faculty feedback on course implementation was positive. We present unPAK as a new network that supports CUREs and research experiences focused on collecting biological data made publicly available to the scientific community. The unPAK CUREs can be tailored to address instructor interests or pedagogical needs while involving students in research investigating quantitative plant phenotypes.</p
Image-Subtraction Photometry of the Globular Cluster M3: identification of new double-mode RR Lyrae stars
We have applied the image subtraction method to the M3 dataset previously
analyzed by Corwin & Carney (2001; CC01). The new analysis produced light
curves and periods for 15 variables, bringing to 222 the total number of RR
Lyrae stars in CC01 M3 dataset. We have identified three new candidate
double-mode (RRd) variables (V13, V200, and V251) in M3. Of the newly
discovered RRd's V13 is unusual in that it has the fundamental as the dominant
pulsation mode. Two of the new candidate RRd's (V13 and V200) have period
ratios as low as 0.738-0.739. They lie separated from all previously known
RRd's in the Petersen diagram, in positions implying a large spread in mass
and/or, less likely, in heavy element mass fraction, among the M3 horizontal
branch (HB) stars. We explore mass transfer and helium enhancement as possible
explanations for the apparent spread in HB masses. We also note that the masses
derived from the RRd analyses now favor little mass loss on the red giant
branch. V200 has changed its dominant pulsation mode from fundamental to first
overtone, while V251 has changed its dominant mode from first overtone to
fundamental in the interval 1992 to 1993. Together with M3-V166 this is the
first time that RRd variables are observed to switch their dominant pulsation
modes while remaining RRd's. The phenomenon is found to occur in a one year
time-span thus suggesting that these stars are undergoing a rapid evolutionary
phase, and that both redward and blueward evolution may take place among the HB
stars in M3. The unusual behavior of the M3 RRd's is discussed and compared to
that of the RRd's identified so far in globular clusters and in the field of
our and other Local Group galaxies. We find lack of correlation between the
presence of RRd variables and any of the cluster structural parameters.Comment: 38 pages, 16 figures, AJ in pres
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Measurement of the underground atmospheric muon charge ratio using the MINOS Near Detector
The magnetized MINOS Near Detector, at a depth of 225 mwe, is used to measure the atmospheric muon charge ratio. The ratio of observed positive to negative atmospheric muon rates, using 301 days of data, is measured to be 1.266±0.001(stat)_(-0.014)^(+0.015)(syst). This measurement is consistent with previous results from other shallow underground detectors and is 0.108±0.019(stat+syst) lower than the measurement at the functionally identical MINOS Far Detector at a depth of 2070 mwe. This increase in charge ratio as a function of depth is consistent with an increase in the fraction of muons arising from kaon decay for increasing muon surface energie
Search for Sterile Neutrinos Mixing with Muon Neutrinos in MINOS
We report results of a search for oscillations involving a light sterile neutrino over distances of 1.04 and 735 km in a nu(mu)-dominated beam with a peak energy of 3 GeV. The data, from an exposure of 10.56 x 10(20) protons on target, are analyzed using a phenomenological model with one sterile neutrino. We constrain the mixing parameters theta(24) and Delta m(41)(2) and set limits on parameters of the four-dimensional Pontecorvo-Maki-Nakagawa-Sakata matrix, vertical bar U-mu 4 vertical bar(2) and vertical bar U-tau 4 vertical bar(2), under the assumption that mixing between nu(e) and nu(s) is negligible (vertical bar U-e4 vertical bar(2) = 0). No evidence for nu(mu) -\u3e nu(s) transitions is found and we set a world-leading limit on theta(24) for values of Delta m(41)(2) less than or similar to 1 eV(2)
Measurement of single pi(0) production by coherent neutral-current nu Fe interactions in the MINOS Near Detector
Forward single pi(0) production by coherent neutral-current interactions, vA - \u3e vA pi(0), is investigated using a 2.8 x 10(20) protons-on-target exposure of the MINOS Near Detector. For single-shower topologies, the event distribution in production angle exhibits a clear excess above the estimated background at very forward angles for visible energy in the range 1-8 GeV. Cross sections are obtained for the detector medium comprised of 80% iron and 20% carbon nuclei with (A) = 48, the highest- \u3c A \u3e target used to date in the study of this coherent reaction. The total cross section for coherent neutral-current single pi(0) production initiated by the v(mu) flux of the NuMI low-energy beam with mean (mode) E-v of 4.9 GeV (3.0 GeV), is 77.6 +/- 5.0 (stat)(-) (+15.0)(16.8) (syst) x 10(-40) cm(2) pernucleus. The results are in good agreement with predictions of the Berger-Sehgal model
Measurement of the neutrino mass splitting and flavor mixing by MINOS
Measurements of neutrino oscillations using the disappearance of muon neutrinos from the Fermilab NuMI neutrino beam as observed by the two MINOS detectors are reported. New analysis methods have been applied to an enlarged data sample from an exposure of protons on target. A fit to neutrino oscillations yields values of ,eV for the atmospheric mass splitting and m sin^2!(2 heta) > 0.90 (90%,C.L.) for the mixing angle. Pure neutrino decay and quantum decoherence hypotheses are excluded at 7 and 9 standard deviations, respectively
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