Magnitude Spread Research Articles

The RR Lyrae Distance to the Draco Dwarf Spheroidal Galaxy

We present the first CCD variability study of the Draco dwarf spheroidal galaxy. The data were obtained with the Fred Lawrence Whipple Observatory 1.2 m telescope on 22 nights, over a period of 10 months, covering a 22' × 22' field centered at α = 17h19m575, δ = 57°50'05'' (J2000.0). The analysis of the BVI images produced 163 variable stars, 146 of which were RR Lyrae: 123 RRab, 16 RRc, 6 RRd, and one RR12. The other variables include a SX Phe star, four anomalous Cepheids, and a field eclipsing binary. Using the short distance scale statistical parallax calibration of Gould & Popowski and 94 RRab stars from our field, we obtain a distance modulus of (m - M)0 = 19.40 ± 0.02 (stat) ± 0.15 (syst) mag for Draco, corresponding to a distance of 75.8 ± 0.7 (stat) ± 5.4 (syst) kpc. By comparing the spread in magnitudes of RRab stars in B, V, and I, we find no evidence for internal dust in the Draco dwarf spheroidal galaxy. The catalog of all variables, as well as their photometry and finding charts, is available electronically via anonymous ftp and the World Wide Web. The complete set of the CCD frames is available upon request.

A New Sample of Distant Compact Groups from the Digitized Second Palomar Observatory Sky Survey

We have identified 84 small, high-density groups of galaxies out to z ∼ 0.2 in a region of ∼2000 deg2 around the north Galactic pole using the digitized Second Palomar Observatory Sky Survey. The groups have at least four galaxies satisfying more stringent criteria than those used by Hickson in his pioneering work in 1982: the adopted limiting surface brightness for each group is brighter (24 mag arcsec-2 instead of 26 mag arcsec-2), and the spread in magnitude among the member galaxies is narrower (2 mag instead of 3). We also adopt a slightly modified version of the isolation criterion used by Hickson, in order to avoid rejecting groups with projected nearby faint background galaxies. A 10% contamination rate due to projection effects is expected for this sample based on extensive simulations.

2MASS Observations of Spectroscopically Identified Extragalactic C Stars

We matched spectroscopically identified C stars (from low-resolution objective prism surveys) in the Magellanic Clouds with Two Micron All Sky Survey (2MASS) sources. We confirm that C stars show a large spread in absolute magnitudes, even in the Ks band. We show that the I and Ks magnitude distributions of a population of C stars (in the LMC) have a similar narrow dispersion if the C stars are selected in a well-defined color range. Using magnitude and color criteria, we employ the 2MASS data to identify 26 C stars in the Fornax dwarf spheroidal galaxy. The mean Ks magnitude and the mean bolometric magnitude of C stars are found to be slightly brighter in the LMC and SMC when compared with those of the Fornax dwarf spheroidal galaxy. The difference could be explained by ages and/or abundance differences.

QSAR models using a large diverse set of estrogens.

Endocrine disruptors (EDs) have a variety of adverse effects in humans and animals. About 58,000 chemicals, most having little safety data, must be tested in a group of tiered assays. As assays will take years, it is important to develop rapid methods to help in priority setting. For application to large data sets, we have developed an integrated system that contains sequential four phases to predict the ability of chemicals to bind to the estrogen receptor (ER), a prevalent mechanism for estrogenic EDs. Here we report the results of evaluating two types of QSAR models for inclusion in phase III to quantitatively predict chemical binding to the ER. Our data set for the relative binding affinities (RBAs) to the ER consists of 130 chemicals covering a wide range of structural diversity and a 6 orders of magnitude spread of RBAs. CoMFA and HQSAR models were constructed and compared for performance. The CoMFA model had a r2 = 0.91 and a q2LOO = 0.66. HQSAR showed reduced performance compared to CoMFA with r2 = 0.76 and q2LOO = 0.59. A number of parameters were examined to improve the CoMFA model. Of these, a phenol indicator increased the q2LOO to 0.71. When up to 50% of the chemicals were left out in the leave-N-out cross-validation, the q2 remained significant. Finally, the models were tested by using two test sets; the q2pred for these were 0.71 and 0.62, a significant result which demonstrates the utility of the CoMFA model for predicting the RBAs of chemicals not included in the training set. If used in conjunction with phases I and II, which reduced the size of the data set dramatically by eliminating most inactive chemicals, the current CoMFA model (phase III) can be used to predict the RBA of chemicals with sufficient accuracy and to provide quantitative information for priority setting.

$\vec{ UBVI}$ imaging photometry of NGC 6231

CCDUBVIphotometry in the eld of the open cluster NGC 6231 was obtained for 1060 stars down to V 19 mag. Memberships, reddening, distance and age of this cluster were investigated. Its lower sequence dis- plays a notorious bend atV 13:5 mag followed by a high number of faint stars showing a large magnitude spread at constant colour. This distribution of stars does not seem to be produced by a mere accumulation of eld stars seen in the direction of the cluster but by a real star excess in the zone. The evidence suggests these stars are serious candidates to be cluster members caught in their way to- wards the ZAMS. Fitting them with pre main sequence isochrones an age spread of about 10 Myr is obtained. The luminosity and mass functions were found to be flat for 7:5 <M V < 1 : 5a nd from 3t o 80M respectively.

Spatial Distribution of Far Infrared and Radio Continuum Emission in Spiral Galaxies

A study of 8 nearby spiral galaxies (NGC 2903, 3079, 3198, 3628, 4303, 4321, 4656 and 6946) is carried out using the radio continuum (RC) and far infrared (FIR) images at 1′ resolution. These images are used to study the radial gradients in the ratios of FIR to RC (Q60 and Q100), warm dust temperature (Td(60/100)) etc. The main results are illustrated with NGC 2903 as an example in Fig. 1, where azimuthally averaged quantities are plotted. Td(60/100) decreases away from the center (45–25 K), increasing again by ∼ 5 K in outer galaxies. Typically Q60 decreases by a factor of three away from the center in a given galaxy, but has an order of magnitude spread in the pixel values over all the galaxies. In contrast, Q100 shows flatter gradient, which is expected from the observed temperature gradient. 20 cm RC emission profile is also shown in Fig. 1. The RC and FIR profiles can be fitted by a combination of central gaussian and exponential disk components. In general RC and FIR have about the same fraction of exponential component with the exception of NGC 3628, in which the FIR is dominated by the gaussian while the RC is mostly disk component (see Fig. 2). In 5 of the remaining 7 galaxies, the exponential component contributes &gt; 50% of the total. In general RC scale lengths are larger than the FIR.

Deep ROSAT HRI observations of the Orion nebula region

We present results from three deep ROSAT high-resolution imager observations of the Orion Nebula star-forming region. The X-ray images contain over 1500 cataloged stars in a roughly 0.8 sq deg region centered on the Trapezium. In all, 389 distinct X-ray sources have been detected, at least two-thirds of which are associated with a single proper-motion cluster member. X-ray emission is detected from stars of all spectral types, from massive O- and B-type components of the Trapezium to the coolest, low-mass pre-main-sequence (PMS) stars. In this paper we focus primarily on X-ray emission from the late-type PMS stars. Of the approximately 100 late-type cluster members with measured spectral types, approximately three-fourths have been detected; we have derived X-ray luminosity upper limits for the remaining stars. We found coronal X-ray emission turns on around spectral type F6, with the upper envelope of activity increasing with deceasing effective temperature. When plotted in an X-ray luminosity versus bolometric luminosity diagram, late-type PMS stars lie below a 'saturation' line corresponding to L(sub x)/L(sub bol) approximately 10(exp -3). For approximately solar-mass PMS stars, we find a median X-ray luminosity approximately 1 x 10(exp 30) ergs/s. The late G, K, and M stars exhibit nearly a two order of magnitude spread in X-ray luminosity and in L(sub x)/L(sub bol) at a given effective temperature. Plots of X-ray activity versus v sin i rotational velocity and rotational period appear to show no clear dependence of activity on rotation. However, because only a small fraction of late-type PMS stars in the Orion Nebula have measured v sin i or P(sub rot) and because of uncertainties in L(sub x) and L(sub x)/L(sub bol), we believe the data are not conclusive on this point. Light curves of the detected X-ray sources have revealed at least 10 strong X-ray flares with characteristic rise times greater than or approximately equal to 1 hr and decay times ranging from approximately 2 to 12 hr. All the flares have X-ray energies in excess of 3 x 10(exp 35) ergs. Many of the X-ray sources associated with late-type cluster members have been observed in more than one ROSAT HRI exposure, allowing us to look for variability on the approximately 1 yr timescale between HRI observations. A statistical analysis of the resulting count rate ratios suggests that at least one-fourth of the late-type cluster stars are significantly variable on this timescale.

On a possible control mechanism for solar wind outflow velocity from coronal holes

In this paper we give an explanation for a control mechanism for velocityV of solar wind (SW) streams for coronal holes (CHs) based on the idea suggested by Rudenko and Fainshtein (1993). In accordance with that idea, the difference of values ofV in high-speed SW streams from different CHs is due to the spread in magnitude of magnetic fieldBa in the region of acceleration of such streams near the Sun. In this case, with increasing magnitude ofBa, there is an increase in velocity of the high-speed stream.

The Evolution of Stellar Coronae: Initial Results from a ROSAT PSPC Observation of IC 2391

A 23 ks ROSAT PSPC image of the young star cluster, IC 2391, reveals 76 soft x-ray sources with L(sub x)(0.2-2.0 keV) greater than or equal to 2 x 10(exp 28) ergs/s in the direction of the cluster center. Nineteen of these sources are associated with known cluster members. We find that x-ray emission from the IC 2391 B stars deviates widely from the L(sub x)/L(sub bol) = 10(exp -7) relation based on Einstein observations of O and early B stars. Instead, we observe a wide range in L(sub x) with an order of magnitude spread at any given mass and no apparent dependence on spectral type. A comparison of the spread of L(sub x) as a function of B-V for low-mass stars between IC 2391 and the much older Hyades cluster shows that despite the factor of approx. 10 difference in their ages, these two clusters exhibit very similar dispersions in levels of stellar activity. We conclude that the low-mass stars in IC 2391 have arrived on the ZAMS with a wide range of coronal activity levels, from very strong to very weak, and that existing empirical activity-age scaling laws therefore cannot be valid.

Prevalence of Pigment Dispersion Syndrome in a Population Undergoing Glaucoma Screening

The prevalence of pigment dispersion syndrome is thought to be relatively uncommon. Extrapolation of prevalences from glaucoma practices would suggest about 25,000 to 220,000 persons in the United States, an order of magnitude spread. By performing two population screenings that included slit-lamp examination, we detected pigment dispersion syndrome in 18 of 934 individuals. Sixteen of these were white, so that the prevalence of pigment dispersion syndrome in this group was 2.45%. We suggest that many more persons than previously believed may be at risk to develop pigment dispersion.

Lithium in F stars of known age

High resolution spectra of 25 F stars in visual binary systems were obtained with the Canada-France-Hawaii Telescope in a search for a correlation between Li abundance and the age of F stars. Computerized scans were made for equivalent widths of the Li 6707 A resonance, the Ca I 6717 A line and five neighboring Fe I lines. Stars cooler than 6300 K exhibited an order of magnitude spread in Li abundance, symptomatic of age-dependent depletion of Li in late F and early G stars. Li was depleted by factors of 6-20 in stars with temperatures from 6300-6700 K, a depletion/temperature pattern also seen in Hyades and mid-F stars, and which may be affected by the presence of companion objects. 21 references.

Shock acceleration of electrons and ions in solar flares

The simultaneous first-order Fermi shock acceleration of electrons, protons, and alpha particles are compared to observations of solar energetic particle events. For each event, a unique shock compression ratio in the range of approximately 1.6-3 produces spectra in good agreement with observation. The range in compression ratios predicts that the more than five orders of magnitude spread in electron-to-proton intensity ratios observed at MeV energies is compressed to about three orders of magnitude at an assumed injection energy of 100 keV. The remaining spread can be accounted for with a modest range of injection conditions. The model predicts that the acceleration time to a given energy will be approximately equal for electrons and protons, and for reasonable solar parameters, can be on the order of 1 s to approximately 100 MeV. 37 references.

Macroscopic structure of the spectra of hot stars in the ultraviolet

Observational material from Orion-2 is used to obtain new results on the macroscopic structure of the continuous spectra of 26 hot B2-A3 stars in the ultraviolet region 2000-3700 A. In particular, a new proof is found that the depression of the continuum in the region near 2400 A is indeed different for different stars of strictly the same spectral subclass and luminosity class and may fluctuate in an appreciable range. It is noted that the depression itself comes about as a result of additional absorption in a circumstellar cloud. The observed spread in the magnitudes of the depression can therefore be interpreted as a spread in the thickness (optical thickness) of the circumstellar cloud on the transition from one star to another. A list of hot stars for which the existence of circumstellar clouds can be regarded as probable is included.

Amorphous FeF3: a non-crystalline magnet with antiferromagnetic interactions

Susceptibility and magnetisation curves for amorphous FeF3 indicate the presence of strong antiferromagnetic exchange coupling which would normally lead to a Neel temperature of the order of 300K in a crystalline lattice. In fact the appearance of remanence and an irreversible susceptibility indicate that spin freezing sets in only below Tf=29K, but there is no sharp phase transition. Mossbauer measurements indicate that the magnetic order is speromagnetic. A low value of the molar Curie constant measured in the range 50-300K (3.54) may be explained by assuming a spread in magnitude of the antiferromagnetic interactions. The results are discussed in terms of magnetic frustration.

Aluminum Wire to Thick-Film Connections for High-Temperature Operation

Hybrid microcircuits in geothermal instrumentation must operate from room temperature to 300°C. Bond failure occurred during operation of initial geothermal circuits due to intermetallic growth at the aluminum wire-to-gold conductor interface. To remedy this problem, two wire bonding techniques have been qualified in high-temperature aging tests: 1) ultrasonic bonding of aluminum wire directly to modified fritless gold conductor inks (DuPont 9910, AVX 3520, and TFS A328) and 2) insertion of a I mil diffusion barrier pad between the thick film and the aluminum wire. Both systems allow 100-1000 h operation at 300°C. Three alloys of wire were tested: pure aluminum, aluminum with I percent silicon, and aluminum with 1 percent magnesium. The degradation rates differed greatly with pure aluminum being the least tolerant to temperature aging and wire with 1 percent silicon faring best. Because thick-film surfaces tend to be harder than thin-film surfaces, hardened aluminum wire (elongation 0.5 percent) formed bonds with less pad deformation and, consequently, with higher pull strengths than standard bonding wire (elongation 1-3 percent). Comparison of wire bonds aged at three temperatures (250, 300, and 350°C) demonstrated several orders of magnitude spread in degradation rates; for 1000-h bond lifetime, 300°C was found to be about the highest allowed operational temperature for direct bonding to gold. Disks of kovar and nickel of l-mil thickness and 30 mils diam were used as diffusion barriers between the gold and aluminum. Evaporated on one side of each disk was a 1 µm gold thin film for thermocompression bonding to the thick film; the other side received an evaporated aluminum film for wire bonding. Aging for 1000 h up to 350°C produced no increase in bond resistance for any of the three wire alloys tested. Some decrease in pull strength with time was noticed but was attributed to annealing of the wire.

A study of M-type stars in Cygnus.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A study of M-type stars in Cygnus. Nassau, J. J. ; van Albada, G. B. Abstract This investigation is a continuation of our work in the infra-red spectra and magnitudes for M giants in the clear region of Cygnus. The primary additions to the observational data were derived by securing 20 objective prism spectral plates for our survey. The limiting magnitudes for which we believe our data to be complete is 13.5 infra-red, although a number of stars were classified down to 14.5. The classification of the M stars was based solely on the TiO bands, while the carbon stars were identified from the bands of CN. A new band near X 7950 has been utilized in the identification of S stars. A band in the same spectral region has been observed in several late M `s, notably variables. The search for M stars has been carried out in a relatively clear region in Cygnus at galactic longitude 430 and latitude 4?o. The area which is in the form of a rectangle, perpendicular to the celestial equator covers 2.28 square degrees. In this area 709 M stars were identified, four carbon stars and two S stars, among them several new variables. The number of M stars per square degree is 311, while at the galactic latitude of 9?2 and approximately the same longitude the corresponding number was 31. Even within the field itself a concentration toward the galactic plane is apparent. The median apparent infra-red magnitude of the Mo stars at galactic latitude 40 is 13.1 which value decreases with advancing spectral type to 11.3 at M4. This is in agreement with the absolute infra-red magnitudes, derived from the Mt. Wilson spectroscopic absolute magnitudes, which give -1.1 for Mo and -2.9 for M4. For the later M types this relation does not seem to exist since the observed median magnitudes remain stationary after M4. From our material it was possible to obtain the spectrum intrinsic color relation for all the M's, as follows: at Mo 1.1. (photographic minus infra-red magnitude) equal to 2.8, at M~ I.I. equal to 4.3. The amount of interstellar absorption of the region was found to be equal to 0.10 mag./kpc infra-red, corresponding to about 0.22 mag.!kpc in the photographic region. The unevenness in the surface distribution of M stars indicates local regions of much heavier obscuration. A density analysis has been made of 627 stars from Mo to M4. At a distance of 2 kpc from the sun the number of stars is 20 X 10-6 stars per cubic parsec. At 6 kpc a value of 8 X 10-6 is reached. These numbers vary slightly with different assumptions in absorption and absolute magnitude spread. Warner and Swasey Observatory, Case Institute of Technology, Cleveland, Ohio. Publication: The Astronomical Journal Pub Date: 1948 DOI: 10.1086/106157 Bibcode: 1948AJ.....54Q..46N full text sources ADS |