English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

There are some strange quasars with multiple Gaia detections or observed withabnormal astrometric characteristics, such as with large proper motions orsignificant astrometric noises. Those strange quasars could be potentialcandidates of quasar-star pairs, dual quasars (DQs), or lensed quasars (LQs).Searching for both DQs and LQs is of great importance in many fields ofastrophysics. Here in this work, we select 143 SDSS spectroscopically confirmedquasars that have multiple Gaia EDR3 detections within 1 arcsec of the SDSSquasar' position. We apply several optical identification methods to classifythis sample. We firstly exclude 65 quasar-star pairs via their stellar featuresincluding their parallaxes and proper motions, stellar features in the SDSSspectra, or via the colour-colour diagram. Based on the spectral-fittingresults, we find 2 DQ candidates, one of which presents a double-peaked [O III]emission line feature and the other shows a broad $H_{\beta}$ velocity offset($\sim$ 870 $ km s^{-1} $) relative to the [O III] $\lambda$5007 line. Via thecolour difference method, we further find 56 LQ candidates with similar coloursin their multiple images. We also cross-match 143 objects with the HST archiveand find 19 targets with archival HST images. Our classification results ofthose 19 targets are mainly consistent with previous works.

Strange Quasar Candidates with Abnormal Astrometric Characteristics from Gaia EDR3 and SDSS (SQUAB-II): Optical Identifications