Detection of the Red Giant Branch Stars in M82 Using the Hubble Space Telescope

We present color-magnitude diagrams and luminosity functions of stars in two halo regions of the irregular galaxy in M82, based on F555W and F814W photometry taken with the Hubble Space Telescope and Wide Field Planetary Camera 2. The I-band luminosity function shows a sudden jump at I~23.95 mag, which is identified as the tip of the red giant branch (TRGB). Adopting the Lee et al. (1993) calibration of the TRGB based on the RR Lyrae distances to Galactic globular clusters, we obtain the distance modulus of (m-M)_0=27.95 +- 0.14 (random) +- 0.16 (systematic) mag. This corresponds to a linear distance of 3.9 +- 0.3 (random) +- 0.3 (systematicf) Mpc, which agrees well with the distance of M81 deteremined from the HST observations of the Cepheid variable stars. In addition, we observe a significant number of stars apparently brighter than the TRGB. However, with the current data, we cannot rule out whether these stars are blends of fainter stars, or are indeed intermediate-age asymptotic giant branch stars.Comment: 8 figure

Growth Performance, Yields and Economic Benefits of Nile Tilapia Oreochromis niloticus and Kales Brassica oleracea Cultured under Vegetable-Fish Culture Integration

An experiment was conducted for 210 days to demonstrate the role of vegetable-fish culture integration in the growth, yields and economic benefits of fish and vegetables. Two 200 m2 earthen fishponds were stocked with Nile tilapia Oreochromis niloticus at 20,000 fish fingerlings per hectare. Pond A was fertilized with chicken manure and stocked fish fed on 35% crude protein supplementary diet referred to here as treated fish pond (TFP). Another fish pond was not fertilized and the fish stocked in it did not receive any supplementary diet referred to here as non treated fish pond (NTFP). Twelve vegetable plots of 7.2 x 3 m were planted with kale seedlings at a spacing of 0.45 x 0.6 m. The first, second and third sets of three vegetable plots were irrigated by water from stream (SW), treated fish pond (TFP) and non treated fish pond (NTFP) respectively. The last three vegetable plots were not irrigated (NI). Sampling of kale leaves was done by removal of the lowest three leaves per plant every four days. Results showed that fish reared under integrated systems attained significantly higher growth than those reared under non integrated systems (t-test, t=14.38, d.f. = 118, P<0.001). One way Analysis of Variance showed a significant difference in kale leaf yields and income (ANOVA: F=63.17; P<0.05; d.f.=3) among plots receiving different sources of water with plots receiving water from treated fish pond (TFP) attaining highest yield and income. Gross and net yields of 2,806.969±198 and 2706.569±194 kgha-1 (for fish) and 51,970.49 and 51,968.63 kgha-1 (for vegetables) respectively attained were highest from integrated than non-integrated systems. Partial enterprise budget analysis showed that net returns were higher from integrated than non integrated systems. Results from this study demonstrate that fish farmers could improve yields and profits by integrating fish farming with other on-farm activities.Tanz. J. Sci. Vol. 37 2011, 37-4

Cepheid and Tip of the Red Giant Branch Distances To the Dwarf Irregular Galaxy IC10

We present color-magnitude diagrams and luminosity functions of stars in the nearby galaxy IC 10, based on VI CCD photometry acquired with the COSMIC prime-focus camera on the Palomar 5m telescope. The apparent I-band luminosity function of stars in the halo of IC 10 shows an identifiable rise at I~21.7 mag. This is interpreted as being the tip of the red giant branch (TRGB) at M_V~-4 mag. Since IC 10 is at a very low Galactic latitude, its foreground extinction is expected to be high and the uncertainty associated with that correction is the largest contributor to the error associated with its distance determination. Multi-wavelength observations of Cepheid variable stars in IC 10 give a Population I distance modulus of 24.1 +- 0.2 mag, which corresponds to a linear distance of 660 +- 66 kpc for a total line-of-sight reddening of E(B-V) = 1.16 +- 0.08 mag, derived self-consistently from the Cepheid data alone. Applying this Population I reddening to the Population II halo stars gives a TRGB distance modulus of 23.5 +- 0.2 mag, corresponding to 500 +- 50 kpc. We consider this to be a lower limit on the TRGB distance. Reconciling the Cepheid and TRGB distances would require that the reddening to the halo is $\Delta$E(B-V) = 0.31 mag lower than that into the main body of the galaxy. This then suggests that the Galactic extinction in the direction of IC10 is (B-V) ~ 0.85

Infrared Spectra of the Subluminous Type Ia Supernova SN 1999by

Near-infrared (NIR) spectra of the subluminous Type Ia supernova SN 1999by are presented that cover the time evolution from about 4 days before to 2 weeks after maximum light. Analysis of these data was accomplished through the construction of an extended set of delayed detonation (DD) models covering the entire range of normal to subluminous SNe Ia. The explosion, light curves, and time evolution of the synthetic spectra were calculated self-consistently for each model, with the only free parameters being the initial structure of the white dwarf and the description of the nuclear burning front during the explosion. From these, one model was selected for SN 1999by by matching the synthetic and observed optical light curves, principally the rapid brightness decline. DD models require a minimum amount of burning during the deflagration phase, which implies a lower limit for the 56Ni mass of about 0.1 M☉ and consequently a lower limit for the SN brightness. The models that best match the optical light curve of SN 1999by were those with a 56Ni production close to this theoretical minimum. The data are consistent with little or no interstellar reddening [E(B-V) ≤ 0.12 mag], and we derive a distance of 11 ± 2.5 Mpc for SN 1999by, in agreement with other estimates. Without any modification, the synthetic spectra from this subluminous model match reasonably well the observed IR spectra taken on 1999 May 6, 10, 16, and 24. These dates correspond roughly to -4, 0, 6, and 14 days after maximum light. Prior to maximum, the NIR spectra of SN 1999by are dominated by products of explosive carbon burning (O, Mg) and Si. Spectra taken after maximum light are dominated by products of incomplete Si burning. Unlike the behavior of normal Type Ia SNe, lines from iron-group elements begin to show up only in our last spectrum taken about 2 weeks after maximum light. The implied distribution of elements in velocity space agrees well with the DD model predictions for a subluminous SN Ia. Regardless of the explosion model, the long duration of the phases dominated by layers of explosive carbon and oxygen burning argues that SN 1999by was the explosion of a white dwarf at or near the Chandrasekhar mass. The good agreement between the observations and the models without fine-tuning a large number of free parameters suggests that DD models are a good description of at least subluminous Type Ia SNe. Pure deflagration scenarios or mergers are unlikely, and helium-triggered explosions can be ruled out. However, problems for DD models still remain, since the data seem to be at odds with recent three-dimensional models of the deflagration phase that predict significant mixing of the inner layers of the white dwarf prior to detonation. Possible solutions include the effects of rapid rotation on the propagation of nuclear flames during the explosive phase of burning or extensive burning of carbon just prior to the runaway

The interferon-inducible antiviral protein Daxx is not essential for interferon-mediated protection against avian sarcoma virus

BACKGROUND: The antiviral protein Daxx acts as a restriction factor of avian sarcoma virus (ASV; Retroviridae) in mammalian cells by promoting epigenetic silencing of integrated proviral DNA. Although Daxx is encoded by a type I (α/β) interferon-stimulated gene, the requirement for Daxx in the interferon anti-retroviral response has not been elucidated. In this report, we describe the results of experiments designed to investigate the role of Daxx in the type I interferon-induced anti-ASV response. FINDINGS: Using an ASV reporter system, we show that type I interferons are potent inhibitors of ASV replication. We demonstrate that, while Daxx is necessary to silence ASV gene expression in the absence of interferons, type I interferons are fully-capable of inducing an antiviral state in the absence of Daxx. CONCLUSIONS: These results provide evidence that Daxx is not essential for the anti-ASV interferon response in mammalian cells, and that interferons deploy multiple, redundant antiviral mechanisms to protect cells from ASV

The Tip of the Red Giant Branch Distance to the Large Magellanic Cloud

We present the I-band luminosity function of the red giant branch stars in the Large Magellanic Cloud (LMC) using the data from the Magellanic Clouds Photometric Survey (Zaritsky, Harris & Thompson, 1997). Selecting stars in uncrowded, low-extinction regions, a discontinuity in the luminosity function is observed at I_0 = 14.54 mag. Identifying this feature with the tip of the red giant branch (TRGB), and adopting an absolute TRGB magnitude of -4.05 +- 0.04 mag based on the calibration of Lee, Freedman & Madore (1993), we obtain a distance modulus of 18.59 +- 0.09 (random) +- 0.16 (systematic) mag. If the theoretical TRGB calibration provided by Cassisi & Salaris (1997) is adopted instead, the derived distance would be 4% greater. The LMC distance modulus reported here, 18.59 +- 0.09, is larger by 0.09 mag (1-sigma) than the value that is most commonly used in the extragalactic distance scale calibrated by the period-luminosity relation of the Cepheid variable stars. Our TRGB distance modulus agrees with several RR Lyrae distances to the LMC based on HIPPARCOS parallaxes. Finally, we note that using the same MCPS data, we obtain a distance modulus of 18.29 +- 0.03 mag using the red clump method, which is shorter by 0.3 mag compared to the TRGB estimate.Comment: 19 pages, 5 figure

Redshifts for 2410 Galaxies in the Century Survey Region

The `Century Survey' strip covers 102 square degrees within the limits 8.5h \leq \alpha_{1950} \leq 16.5h, 29.0 degrees \leq \delta_{1950} \leq 30.0 degrees. The strip passes through the Corona Borealis supercluster and the outer region of the Coma cluster. Within the Century Survey region, we have measured 2410 redshifts which constitute four overlapping complete redshift surveys: (1) 1728 galaxies with Kron-Cousins R_{phot} \leq 16.13 covering the entire strip, (2) 507 galaxies with R_{phot} \leq 16.4 in the right ascension range 8h 32m \leq \alpha_{1950} \leq 10h 45m, (3) 1251 galaxies with absorption- and K-corrected R_{CCD, corr} \leq 16.2 covering the right ascension range 8.5h \leq \alpha_{1950} \leq 13.5h and (4) 1255 galaxies with absorption- and K-corrected V_{CCD, corr} \leq 16.7 also covering the right ascension range 8.5h \leq \alpha_{1950} \leq 13.5h. All of these redshift samples are more than 98 % complete to the specified magnitude limit.Comment: 18 pages, 9 figures, 3 tables, 2 abbreviated tables. In press, to appear in Astronomical Journal, Dec. 2001 issu

Variable stars in the field of the Hydra II ultra-faint dwarf galaxy

We report the discovery of one RR Lyrae star in the ultra--faint satellite galaxy Hydra II based on time series photometry in the g, r and i bands obtained with the Dark Energy Camera at Cerro Tololo Interamerican Observatory, Chile. The RR Lyrae star has a mean magnitude of $i = 21.30\pm 0.04$ which translates to a heliocentric distance of $151\pm 8$ kpc for Hydra II; this value is $\sim 13\%$ larger than the estimate from the discovery paper based on the average magnitude of several blue horizontal branch star candidates. The new distance implies a slightly larger half-light radius of $76^{+12}_{-10}$ pc and a brighter absolute magnitude of $M_V = -5.1 \pm 0.3$, which keeps this object within the realm of the dwarf galaxies. The pulsational properties of the RR Lyrae star ($P=0.645$ d, $\Delta g = 0.68$ mag) suggest Hydra II may be a member of the intermediate Oosterhoff or Oosterhoff II group. A comparison with other RR Lyrae stars in ultra--faint systems indicates similar pulsational properties among them, which are different to those found among halo field stars and those in the largest of the Milky Way satellites. We also report the discovery of 31 additional short period variables in the field of view (RR Lyrae, SX Phe, eclipsing binaries, and a likely anomalous cepheid). However, given their magnitudes and large angular separation from Hydra II, they must be field stars not related to Hydra II.Comment: Revised version after comments from the referee. Accepted for publication in A