Star Proper Motions Based on Two-epoch Observations from the SDSS and DESI Imaging Surveys

Abstract In this study, we present the construction of a new proper-motion catalog utilizing the photometric data from the Sloan Digital Sky Survey (SDSS) and Dark Energy Spectroscopic Instrument (DESI) imaging surveys, with a median time baseline of about 13 yr. To mitigate systematic errors, the DESI galaxy positions are employed to establish a reference frame and to correct the position-, magnitude-, and color-dependent discrepancies between the SDSS and DESI imaging data sets. Spanning 12,589 deg 2 , the catalog encompasses about 223.7 million non-Gaia objects down to m r ∼ 23. Based on 734,000 quasars, the assessment of the global systematic errors in the DESI−SDSS proper-motion catalog yields values of 0.06 mas yr −1 for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>μ</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> </mml:math> and 0.12 mas yr −1 for μ δ . The catalog exhibits precision surpassing 3.4 mas yr −1 , albeit varying with position, color, and magnitude. An additional evaluation employing approximately 2644 distant star samples yields an overall precision of approximately 2.5 and 2.9 mas yr −1 for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>μ</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> </mml:math> and μ δ , respectively. Further comparisons with proper motions from SDSS Stripe 82 reveal a strong consistency between the two data sets. As a practical application, we utilize fainter non-Gaia objects in our catalog to update the proper motions of 15 star clusters. The resulting proper motions for these clusters exhibit excellent consistency with those derived from Gaia data. Our proper-motion measurements, characterized by a deeper limiting magnitude, stand as a valuable complement to the Gaia data set.