Observations of 226 AGNs in the near-infrared J, H, and K' bands are presented along with the analysis of the observations for variability. Our sample consists mainly of Seyfert 1 AGNs and QSOs. About a quarter of the objects in each category are radio loud. The AGNs in the entire sample have the redshifts spanning the range from z=0 to 1, and the absolute magnitudes from M_B_=-29 to -18. All the objects were observed twice, and their variability was measured by differential photometry. A reduction method of differential photometry, optimized to the analysis of extended images, has been developed. The systematic error in variability arising from AGNs of highly extended images is estimated to be less than 0.01mag in each of the J, H, and K' bands. The systematic error arising from the flat-fielding is negligible for most AGNs, although it is more than 0.1mag for some particular cases. The overall average flat-fielding error is 0.03mag for the image pairs. We find that these systematic errors are superseded by statistical errors, and the overall average total systematic and statistical errors amounts to 0.05mag in the measured variability in each band.
Long-term JHK light curves have recently become available for large numbers of the more luminous stars in the Small Magellanic Cloud (SMC). We have used these JHK light curves, along with OGLE (Optical Gravitational Lensing Experiment) V and I light curves, to examine the variability of a sample of luminous red giants in the SMC which show prominent long secondary periods (LSPs). The origin of the LSPs is currently unknown. In oxygen-rich stars, we found that while most broad-band colours (e.g. V- I) get redder when an oxygen-rich star dims during its LSP cycle, the J-K colour barely changes and sometimes becomes bluer. We interpret the J-K colour changes as being due to increasing water vapour absorption during declining light caused by the development of a layer of dense cool gas above the photosphere. This result and previous observations which indicate the development of a chromosphere between minimum to maximum light suggest that the LSP phenomenon is associated with the ejection of matter from the stellar photosphere near the beginning of light decline. We explore the possibility that broad-band light variations from the optical to the near-infrared regions can be explained by either dust absorption by ejected matter or large spots on a rotating stellar surface. However, neither model is capable of explaining the observed light variations in a variety of colour-magnitude diagrams. We conclude that some other mechanism is responsible for the light variations associated with LSPs in red giants.
We present infrared JHK time series photometry of the variable star RR Lyr, that allows us to construct the first complete and accurate infrared light curves for this star. The derived mean magnitudes are <J>=6.74+/-0.02, <H>=6.60+/-0.03 and <K>=6.50+/-0.02. The <K> magnitude is used to estimate the reddening, the mass, the mean luminosity and the temperature of this variable star. The use of these RR Lyr data provides a more accurate absolute calibration of the P-L_K_-[Fe/H] relation, and a distance modulus (m-M)0=18.48+/-0.11 to the globular cluster Reticulum in the Large Magellanic Cloud.
We combine our previous optical spectroscopic and photometric analysis of 1600 stars located in the Orion Nebula Cluster (ONC) with our own and published near-infrared photometric surveys of the region in order to investigate the evidence for and properties of circumstellar disks. We use the near-infrared continuum excess as our primary disk diagnostic, although we also study sources with Ca II triplet emission and those designated as "proplyds."
The results of a photometric monitoring in the wavelength range 1-20um are presented for 37 oxygen-rich sources. The sample contains optically identified miras (13), M-type supergiants (3), type II OH/IR sources (20) and one unidentified object. Each source was observed on at least 13 occasions (up to 42) over a lapse of at least 1250 days (up to 2150) between 1984 and 1990 with the ESO 1-m telescope equipped with its standard infrared photometer.
We present the JHKLM photometry for 22 hot stars, 11 of which were identified in the GCVS. For all of the observed objects, we have estimated the interstellar reddening, angular diameters, and the volume emission measures of their gaseous shalls.
This paper supplements Kerschbaum and Hron (1994), where new JHKL'M observations of 200 Semiregular variables of types SRa and SRb were presented with additional 44 near infrared observations and 5 literature data sets. The total sample was defined in Kerschbaum & Hron (1992, Paper I) by means of a certain limit in bolometric magnitude. From the sample of 350 objects, 303 now have near infrared (NIR) photometry. In total 339 datasets are available because of some multiple observations. A detailed analysis of the whole dataset will be presented in a forthcoming paper.
We present J H K L M photometry for 25 Carbon stars, and 450, 600, 800 and 1100 {mu}m for 12 carbon stars and the S-star W Aql. Carbon stars reside on a different part of the [12-25], [K-L] diagram than O-rich stars. Our work confirms earlier observations and shows this relation to hold up at least [K-L] ~ 8mag.
