Multiband Comparative Study of Optical Microvariability in RL vs. RQ Quasars

We present the results of an optical multi-band (BVR) photometric monitoring program of 22 core-dominated radio-loud quasars (CRLQs) and 22 radio-quiet quasars (RQQs). The aim was to compare the properties of microvariability in both types of quasars. We detected optical microvariability in 5 RQQs and 4 CRLQs. Our results confirm that microvariability in RQQs may be as frequent as in CRLQs. In addition we compare microvariability duty cycles in different bands. Finally, the implications for the origin of the microvariations are briefly discussed.Comment: 17 pages, 14 figures, Accepted for publication in the Astronomical Journa

Reverberation Measurements of the Inner Radius of the Dust Torus in Nearby Seyfert 1 Galaxies

The most intense monitoring observations yet made in the optical (UBV) and near-infrared (JHK) wave bands were carried out for nearby Seyfert1 galaxies of NGC 5548, NGC 4051, NGC 3227, and NGC 7469. Over three years of observations with MAGNUM telescope since early 2001, clear time-delayed response of the K-band flux variations to the V-band flux variations was detected for all of these galaxies. Their H-K color temperature was estimated to be 1500-1800 K from the observed flux variation gradients, which supports a view that the bulk of the K flux should originate in the thermal radiation of hot dust that surrounds the central engine. Cross-correlation analysis was performed to quantify the lag time corresponding to the light-travel distance of the hot dust region from the central engine. The measured lag time is 47-53 days for NGC 5548, 11-18 days for NGC 4051, about 20 days for NGC 3227, and 65-87 days for NGC 7469. We found that the lag time is tightly correlated with the optical luminosity as expected from dust reverberation ($\Delta t \propto L^{0.5}$), while only weakly with the central virial mass, which suggests that an inner radius of the dust torus around the active nucleus has a one-to-one correspondence to central luminosity. In the lag time versus central luminosity diagram, the K-band lag times place an upper boundary on the similar lag times of broad-emission lines in the literature. This not only supports the unified scheme of AGNs, but also implies a physical transition from the BLR out to the dust torus that encircles the BLR. Furthermore, our V-band flux variations of NGC 5548 on timescales of up to 10 days are found to correlate with X-ray variations and delay behind them by one or two days, indicating the thermal reprocessing of X-ray emission by the central accretion flow.Comment: ApJ, March 2006, v639 issue, 24 pages, 33 figures, 10 table

Inner Size of a Dust Torus in the Seyfert 1 Galaxy NGC 4151

The most intense monitoring observations yet made were carried out on the Seyfert 1 galaxy NGC 4151 in the optical and near-infrared wave-bands. A lag from the optical light curve to the near-infrared light curve was measured. The lag-time between the V and K light curves at the flux minimum in 2001 was precisely 48+2-3 days, as determined by a cross-correlation analysis. The correlation between the optical luminosity of an active galactic nucleus (AGN) and the lag-time between the UV/optical and the near-infrared light curves is presented for NGC 4151 in combination with previous lag-time measurements of NGC 4151 and other AGNs in the literature. This correlation is interpreted as thermal dust reverberation in an AGN, where the near-infrared emission from an AGN is expected to be the thermal re-radiation from hot dust surrounding the central engine at a radius where the temperature equals to that of the dust sublimation temperature. We find that the inner radius of the dust torus in NGC 4151 is $\sim$ 0.04 pc corresponding to the measured lag-time, well outside the broad line region (BLR) determined by other reverberation studies of the emission lines.Comment: Accepted for publication in ApJ Letters, 13 pages, 3 figures; Corrected typo

The Transit Light Curve Project. V. System Parameters and Stellar Rotation Period of HD 189733

We present photometry of HD 189733 during eight transits of its close-in giant planet, and out-of-transit photometry spanning two years. Using the transit photometry, we determine the stellar and planetary radii and the photometric ephemeris. Outside of transits, there are quasiperiodic flux variations with a 13.4 day period that we attribute to stellar rotation. In combination with previous results, we derive upper limits on the orbital eccentricity, and on the true angle between the stellar rotation axis and planetary orbit (as opposed to the angle between the projections of those axes on the sky).Comment: Accepted for publication in AJ [21 pages]; minor change

The Type Ic Hypernova SN 2002ap

Photometric and spectroscopic data of the energetic Type Ic supernova (SN) 2002ap are presented, and the properties of the SN are investigated through models of its spectral evolution and its light curve. The SN is spectroscopically similar to the "hypernova" SN 1997ef. However, its kinetic energy [$\sim (4-10) \times 10^{51}$ erg] and the mass ejected (2.5-5 $M_{\odot}$) are smaller, resulting in a faster-evolving light curve. The SN synthesized $\sim 0.07 M_{\odot}$ of $^{56}$Ni, and its peak luminosity was similar to that of normal SNe. Brightness alone should not be used to define a hypernova, whose defining character, namely very broad spectral features, is the result of a high kinetic energy. The likely main-sequence mass of the progenitor star was 20-25 $M_{\odot}$, which is also lower than that of both hypernovae SNe 1997ef and 1998bw. SN 2002ap appears to lie at the low-energy and low-mass end of the hypernova sequence as it is known so far. Observations of the nebular spectrum, which is expected to dominate by summer 2002, are necessary to confirm these values.Comment: 10 pages, 4 figures, accepted for publication in ApJL, 30 April 2002 (minor changes to match the accepted version, with figures being colored

Using a complete spectroscopic survey to find red quasars and test the KX method

We present an investigation of quasar colour-redshift parameter space in order to search for radio-quiet red quasars and to test the ability of a variant of the KX quasar selection method to detect quasars over a full range of colour without bias. This is achieved by combining IRIS2 imaging with the complete Fornax Cluster Spectroscopic Survey to probe parameter space unavailable to other surveys. We construct a new sample of 69 quasars with measured bJ - K colours. We show that the colour distribution of these quasars is significantly different from that of the Large Bright Quasar Survey's quasars at a 99.9% confidence level. We find 11 of our sample of 69 quasars have signifcantly red colours (bJ - K >= 3.5) and from this, we estimate the red quasar fraction of the K <= 18.4 quasar population to be 31%, and robustly constrain it to be at least 22%. We show that the KX method variant used here is more effective than the UVX selection method, and has less colour bias than optical colour-colour selection methods.Comment: 11 pages, 14 figures, accepted for publication in MNRA

Extreme infrared variables from UKIDSS-I. A concentration in star-forming regions

We present initial results of the first panoramic search for high-amplitude near-infrared variability in theGalactic plane.We analyse the widely separated two-epoch K-band photometry in the fifth and seventh data releases of the UKIDSS Galactic plane survey.We find 45 stars with δK > 1 mag, including two previously known OH/IR stars and a Nova. Even though the midplane is not yet included in the data set, we find the majority (66 per cent) of our sample to be within known star-forming regions (SFRs), with two large concentrations in the Serpens OB2 association (11 stars) and the Cygnus-X complex (12 stars). Sources in SFRs show spectral energy distributions that support classification as young stellar objects (YSOs). This indicates that YSOs dominate the Galactic population of high-amplitude infrared variable stars at low luminosities and therefore likely dominate the total high-amplitude population. Spectroscopic follow up of the DR5 sample shows at least four stars with clear characteristics of eruptive premain- sequence variables, two of which are deeply embedded. Our results support the recent concept of eruptive variability comprising a continuum of outburst events with different timescales and luminosities, but triggered by a similar physical mechanism involving unsteady accretion. Also, we find what appears to be one of the most variable classical Be stars. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society

CHARTERING FUNDING AND RETURN ON ASSETS OF GUARANTEE CURRENCY STORES

The study set out to examine the chartering funding and return on assets of Guarantee Currency Stores. The study adopted the ex-post facto research design. The main purpose of the study was to generally evaluate the extent to which chartering funding could be considered as a better option amongst the various options of funding and extent which chartering funding affect the return on assets of guarantee currency stores. Data were collected from the annual reports of the selected Guarantee Currency Stores and the data were analyzed using regression method. The findings revealed that there is positive and significant relationship between funding charter, debt funding and return on asset respectively. Based on the findings, it was concluded that funding charter is one of the major sources of funding any asset as this option of funding ensures ample return on asset. The policy and economic implications are that; Guarantee Currency Stores should think through and judiciously appraise funding charter alternative in the construction of their capital structure as this increases return on asset more than others sources of capital while Machinery Charter Union of Nigeria should create more awareness on the significance of funding charter to encourage those Guarantee Currency Stores seeking for funds to use either funding charter or debt capital taking into reflection the benefits of the two options in terms of improved corporate return on asset.  Article visualizations

OIL VALUE VARIATIONS AND COST-EFFECTIVENESS TOWARDS WEALTH CREATION OF OIL AND GAS VENDING CORPORATIONS

The study investigated the effect of oil value variations and cost-effectiveness towards wealth creation of oil and gas vending corporations. The main objective of the study was to determine whether oil value variation impact on cost-effectiveness in the processes of wealth creation in oil and gas vending corporations in Nigeria. Data were obtained from secondary sources such as annual financial reports of corporations which were within the coverage years of investigation. Simple regression technique was used to analyze the data collected. The findings revealed that, oil value variations do not significantly affect cost-effectiveness in the processes of wealth creation of oil and gas vending corporations under consideration. Based on the findings, the study recommended that the management of companies should devise effective strategies in regulating and controlling the effect of oil value variations on their corporate cost-effectiveness towards wealth creation. JEL: L20; L22; L72  Article visualizations