The Hamburg Quasar Monitoring program (HQM) at Calar Alto I. Low amplitude variability in quasars.
Abstract
HQM is an optical broad-band photometric monitoring program carried out since Sept. 1988. Our main intention is to search for indications of microlensing in a sample of ~100 selected quasars; however, we also want to study the intrinsic variability. We use a CCD camera equipped to the MPIA 1.2m telescope. Fully automatic photometric reduction relative to stars in the frame is done within a few minutes after each exposure, thus interesting brightness changes can be followed in detail. The typical photometric error is 1-2% for a 17.5mag quasar, making HQM the most accurate long-term quasar monitoring program yet carried out. The main results of HQM which we discuss here are: (1) Concerning variability, quasars form two, clearly distinct classes, optically violent variables (OVVs) and non-OVVs. (2) All OVVs are radio loud and probably belong to the blazar class. (3) Non-OVVs have lightcurve gradients of at most several 0.1mag/yr in the quasar restframe and can be well fitted by polynomials of low order. (4) Although our data cover only a relatively short timespan, we conclude that there is a large fraction of quasars which would be undetectable in photographic surveys using optical variability alone as the selection criterium. (5) A broad class of flat-spectrum radio quasars are no blazars, they are even less variable in the optical than radio quiet objects. (6) There is some statistical evidence for microlensing in our sample; if present it does, however, lead only to low lightcurve gradients.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- April 1994
- DOI:
- 10.48550/arXiv.astro-ph/9403048
- arXiv:
- arXiv:astro-ph/9403048
- Bibcode:
- 1994A&A...284..764B
- Keywords:
-
- Astronomical Photometry;
- Gravitational Lenses;
- Quasars;
- Variability;
- Blazars;
- Charge Coupled Devices;
- Data Reduction;
- Light Curve;
- Optical Filters;
- Photometers;
- Statistical Analysis;
- Telescopes;
- Astronomy;
- TECHNIQUES: PHOTOMETRIC;
- QUASARS: GENERAL;
- GRAVITATIONAL LENSES;
- Astrophysics
- E-Print:
- Astron. &