VdB 158

VdB 158 is a faint reflection nebula located in the constellation of Andromeda, at the southern tip of the elongated molecular cloud known as LBN 534 or GAL 110–13.^[1][2] It is illuminated primarily by the hot B-type main-sequence star HD 222142 (B8V),^[3] whose reflected light gives the nebula its characteristic blue hue due to Rayleigh scattering.^[4] The nebula appears as a small, sharply bent structure embedded within the darker filament of GAL 110–13, often described as resembling a cosmic checkmark in wide-field images.^[5]

VdB 158 lies approximately 2° north of the bright star Lambda Andromedae, near the border between Andromeda and Cassiopeia.^[6] Centered on HD 222142, though the associated cloud extends over about 1.5°–2° of sky in a northeast–southwest orientation.^[7] The region is part of the broader Lacerta OB1 star-forming association, several degrees to the west, and is best observed from the Northern Hemisphere during late autumn and winter under dark skies.^[8][9][10]

Due to its low surface brightness, VdB 158 is challenging for visual observation and requires long-exposure astrophotography to capture its details, often revealing the surrounding dark cloud and nearby objects such as the small planetary nebula PK 110–12.1 (discovered by Luboš Kohoutek in 1963).^[11]

VdB 158 forms the brighter, reflective portion at the end of GAL 110–13, an isolated, cometary-shaped molecular cloud roughly 36 light-years (11 parsecs) across and elongated along a position angle pointing toward the O-type star 10 Lacertae (in Lac OB1b).^[12][13] The cloud's unusual 90-degree bend and overall morphology may result from interactions such as cloud–cloud collisions, stellar winds from nearby massive stars, or the aftermath of a supernova explosion within Lac OB1, which could have triggered star formation in the region.^[6] Additional illumination comes from two other B-type stars of spectral class B9V, HD 222046^[14] and HD 222086,^[15] which share proper motion with HD 222142, suggesting they form a small physical group embedded in the cloud.^[6]

The cloud's magnetic field geometry, studied via polarimetric observations of background stars, shows a predominantly toroidal structure aligned with the cloud's long axis, consistent with compression by external radiation or shocks from 10 Lacertae at a projected distance of about 11 parsecs.^[12]