COUNTESS I: A Uniformly Vetted Catalog of Known and New Transiting Exoplanets in the TESS Northern Continuous Viewing Zone

The Transiting Exoplanet Survey Satellite (TESS) has transformed the study of nearby exoplanetary systems; however, its nominal observing strategy limits sensitivity to planets with orbital periods shorter than about 10 days for most parts of the sky. The two TESS Continuous Viewing Zones (CVZs) provide extended temporal baselines that help overcome this limitation, enabling the detection of longer-period (> 10 days) transiting planets around nearby stars. Here, we present COUNTESS, a transit-search pipeline optimized for long-baseline TESS observations that combines multi-sector light curves with heterogeneous cadences, and implements fast-folding BLS period detection, vetting, and statistical validation. As a first application of the pipeline, we conducted a search on the primary and first extended mission photometry in the TESS northern CVZ. For this analysis, we used Gaia DR3 and 2MASS photometry to homogeneously derive a stellar catalog of FGKM stars for the TESS northern CVZ, resulting in a sample of 391,059 stars. We used COUNTESS to search for transiting planets around 26,114 of these stars with TESS-SPOC light curves and assessed its performance, recovering 115 out of 159 known TESS Objects of Interest (TOIs; 0.85 days < P <124.72 days; 1.03 R < R p < 16.35 R). Additionally, we identified 10 new exoplanet candidates (1.20 days < P <34.62 days; 1.73 R < R p < 4.19 R) that passed vetting tests, including two new statistically validated sub-Neptunes, TIC 219893931b and TIC 237254473b. COUNTESS enables extended-baseline TESS analyses and identification of longer-period planets, establishing a foundation for future exoplanet demographic studies, including comparisons with Kepler and K2.