Jørgensen, J. K., Coutens, A., Drozdovskaya, M. N., Lee, J.-E, Plunkett, A. L., Maret, S., Belloche, A., Harsono, D., Telkamp, Z., Cruz-Sáenz de Miera, F., van ’t Hoff, M. L. R., Kóspál, Á., Rao, M., Bergner, J., Jeong, J.-H., Spezzano, S., McGuire, B. A., Nazari, P., Yang, Y.-L., Yun, H.-S., Andreu, A., Ferrer Asensio, J., Kim, C.-H., Ligterink, N. F. W., Lin, Y., Liu, S.-Y., Lützen, M., Marchand, P., Xue, C., and Zeng, S.

This paper presents an overview and first results from the ALMA Large Program, Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS): the chemical inventory of complex organic molecules in the earliest stages of star formation remains poorly constrained, partly because past studies focused on individual sources or limited molecule sets. COMPASS addresses this by conducting unbiased, high-resolution spectral surveys of 11 Class 0/I protostars across a spectral range of 279–312 GHz. These observations map the warm gas around embedded protostars and reveal distinct chemical fingerprints for each source. Initial results highlight variations in the abundances of oxygen- and nitrogen-bearing molecules, though typically below an order of magnitude. Fully quantifying these differences requires COMPASS’s broad spectral coverage and detailed analysis of the thousands of detected lines, which will be presented in future studies.

Plunkett, A. L., Maret, S., Harsono, D., Jørgensen, J. K., Coutens, A., Drozdovskaya, M. N., Lee, J.-E., Belloche, A., Cruz-Sáenz de Miera, F., van 't Hoff, M. L. R., Jeong, J.-H., Kim, C.-H., Kóspál, Á., Lützen, M., McGuire, B. A., Nazari, P., Spezzano, S., Telkamp, Z., Yang, Y.-L., Yun, H.-S., Andreu, A., Bergner, J., Ferrer Asensio, J., Ligterink, N. F. W., Lin, Y., Liu, S.-Y., Marchand, P., Rao, M., and Zeng, S.

ALMA is uniquely suited to probing the chemical makeup of warm gas around embedded solar-type protostars. The COMPASS program has therefore conducted an extensive spectral survey of eleven such regions to study how environment and evolution shape their chemistry. The paper presents the technical setup of these observations along with the procedures needed to understand and use the resulting data. It outlines the calibration and imaging workflow, including the use of CASA and IMAGER and the strategies adopted to address challenges such as large data volumes and continuum subtraction. It also outlines the strategy toward providing a comprehensive set of data products—ranging from image cubes to extracted spectra and continuum maps—to support future scientific and archival studies.

Coutens, A., Cruz-Sáenz de Miera, F., Jørgensen, J. K., Drozdovskaya, M. N., Lee, J.-E., Plunkett, A. L., Harsono, D., Maret, S., Belloche, A., Ferrer Asensio, J., van 't Hoff, M. L. R., Jeong, J.-H., Kóspál, Á., McGuire, B. A., Nazari, P., Spezzano, S., Telkamp, Z., Yang, Y.-L., Yun, H.-S., Zeng, S., Andreu, A., Bergner, J., Kim, C.-H., Ligterink, N. F. W., Lin, Y., Liu, S.-Y., Lützen, M., Marchand, P., and Rao, M.

Methanol is a key complex organic molecule in star-forming regions, and its deuterated isotopologues provide important constraints on chemical formation pathways during star and planet formation. Using ALMA COMPASS spectral survey data of the low-mass protostar BHR71-IRS1, this study measures the column densities and deuterium fractionation of methanol. The paper presents a detailed LTE analysis of multiple methanol isotopologues identified with CASSIS, including five deuterated species. The results show increasing deuteration with the number of deuterium atoms on the methyl group, with statistically corrected D/H ratios reaching ∼23% for CD₃OH relative to CH₃OH. These trends resemble those seen in other low-mass protostars but differ from eruptive systems, motivating comparable analyses across the full COMPASS sample to assess environmental and evolutionary effects.

Nazari, P., Coutens, A., Jørgensen, J. K., Belloche, A., Plunkett, A. L., Maret, S., Harsono, D., Drozdovskaya, M. N., Lee, J.-E., Cruz-Sáenz de Miera, F., Ferrer Asensio, J., van 't Hoff, M. L. R., Jeong, J.-H., Kóspál, Á., McGuire, B. A., Spezzano, S., Yang, Y.-L., Yun, H.-S., and Zeng, S.

Methyl cyanide is a prominent nitrogen-bearing complex organic molecule in protostellar environments, yet its minor isotopologues have rarely been studied with sufficient spectral coverage and sensitivity. Using ALMA COMPASS observations spanning ~33 GHz toward the low-mass protostar BHR 71 IRS1, this study analyzes a broad set of methyl cyanide isotopologues. The paper presents detections of multiple ¹³C-, ¹⁵N-, and deuterated isotopologues and compares their column density ratios with those in both low- and high-mass star-forming regions. The derived D/H ratios in low-mass sources are similar to each other but about an order of magnitude higher than in Sgr B2(N2), and they increase with the number of deuterium atoms, mirroring trends seen for methanol. These results suggest that methyl cyanide and methanol likely form during similar phases of star formation, a hypothesis that future COMPASS studies will test with larger samples.

Yun, H.-S., Lee, J.-E., Jørgensen, J. K., Coutens, A., Plunkett, A. L., Drozdovskaya, M. N., Belloche, A., Jeong, J.-H., Nazari, P., Yang, Y.-L., van 't Hoff, M. L. R., Maret, S., Cruz-Sáenz de Miera, F., Harsono, D., Kim, C.-H., Kóspál, Á., Lützen, M., Spezzano, S., and Zeng, S.

Complex organic molecules around protostars may either be chemically inherited or reprocessed in situ, but the mechanisms governing their spatial distribution and desorption remain uncertain. Using ALMA COMPASS observations of the low-mass protostar BHR71-IRS1, this study focuses on methanol emission extending beyond the compact hot corino region. The paper presents a spatial and physical characterization of 26 extended CH₃OH lines, identifying emission from cavity walls, shocked knots, and more distant components through Principal Component Analysis (PCA) and LTE calculations. The cavity walls show low excitation temperatures and narrow line widths, while the shocked knots exhibit higher temperatures and column densities. These contrasting properties favor FUV-driven reactive desorption in the cavity walls and shock-induced dust sputtering in the knots.

Jeong, J.-H., Lee, J.-E., Jørgensen, J. K., Coutens, A., Drozdovskaya, M. N., Plunkett, A. L., Belloche, A., Maret, S., Yun, H.-S., Cruz-Sáenz de Miera, F., Harsono, D., van 't Hoff, M. L. R., Kim, C.-H., Kóspál, Á., McGuire, B. A., Nazari, P., Spezzano, S., Yang, Y.-L., and Zeng, S.

Class I methanol masers are known tracers of shocks in star-forming regions, but their prevalence in embedded low-mass protostars has been poorly constrained. Using ALMA COMPASS spectral surveys, this study searches for emission from the newly identified 302.9 GHz class I CH₃OH maser across a sample of 11 protostellar sources. The paper presents the first systematic characterization of the occurrence, spatial distribution, and excitation conditions of this maser in low-mass protostellar environments. Maser emission is detected in 7 of 11 sources, predominantly in young, embedded systems, where it traces knots along outflow cavity walls and bow shocks. Among the surveyed complex organic molecules, acetaldehyde (CH₃CHO) uniquely follows the shocked maser morphology, supporting a scenario of shock-driven chemical enhancement.