Searching Beyond the Obscuring Dust Between the Cygnus-Aquila Rifts for Cepheid Tracers of the Galaxy's Spiral Arms

TL;DR

This study uses newly discovered Cepheids in obscured Galactic regions to refine the Milky Way's spiral structure, revealing deviations from canonical models and providing updated parameters for known Cepheids.

Contribution

It presents the first multiband photometric data for Cepheids beyond the dust obscuration, improving the understanding of the Galaxy's spiral arms and revising parameters for BY Cas.

Findings

Confirmed high extinction (A_V~6 mag) in the region

Cepheids do not trace the main Sagittarius-Carina arm

Spiral features deviate from logarithmic patterns

Abstract

A campaign is described, open to participation by interested AAVSO members, of follow-up observations for newly-discovered Cepheid variables in undersampled and obscured regions of the Galaxy. A primary objective being to use these supergiants to clarify the Galaxy's spiral nature. Preliminary multiband photometric observations are presented for three Cepheids discovered beyond the obscuring dust between the Cygnus & Aquila Rifts (40 \le l \le 50 degrees), a region reputedly tied to a segment of the Sagittarius-Carina arm which appears to cease unexpectedly. The data confirm the existence of exceptional extinction along the line of sight at upwards of A_V~6 magnitudes (d~2 kpc, l~47 degrees), however, the noted paucity of optical spiral tracers in the region does not arise solely from incompleteness owing to extinction. A hybrid spiral map of the Galaxy comprised of classical Cepheids, young open clusters & H II regions, and molecular clouds, presents a consistent picture of the Milky Way and confirms that the three Cepheids do not populate the main portion of the Sagittarius-Carina arm, which does not emanate locally from this region. The Sagitarrius-Carina arm, along with other distinct spiral features, are found to deviate from the canonical logarithmic spiral pattern. Revised parameters are also issued for the Cepheid BY Cas, and it is identified on the spiral map as lying mainly in the foreground to young associations in Cassiopeia. A Fourier analysis of BY Cas' light-curve implies overtone pulsation, and the Cepheid is probably unassociated with the open cluster NGC 663 since the distances, ages, and radial velocities do not match.