================================================================================ JWST Imaging of the Closest Globular Clusters--IV. Chemistry, luminosity and mass functions of the lowest-mass members in the NIRISS parallel fields Libralato M., Gerasimov R., Bedin L., Anderson J., Apai D., Bellini A., Burgasser A. J., Griggio M., Nardiello D., Salaris M., Scalco M., Vesperini E. ================================================================================ Keywords: astrometry – photometry – proper motions – stellar clusters – globular clusters Objects: ----------------------------------------- RA (2000) DE Designation(s) ----------------------------------------- Abstract: We present observations of the two closest globular clusters, NGC 6121 and NGC 6397, taken with the NIRISS detector of JWST. The combination of our new JWST data with archival Hubble Space Telescope (HST) images allows us to compute proper motions, disentangle cluster members from field objects, and probe the main sequence (MS) of the clusters down to <0.1 M_Sun as well as the brighter part of the white-dwarf sequence. We show that theoretical isochrones fall short in modeling the low-mass MS and discuss possible explanations of the observed discrepancies. Our analysis suggests that the lowest-mass members of both clusters are significantly more metal-rich and oxygen-poor than their higher-mass counterparts. It is unclear if the difference is caused by a genuine mass-dependent chemical heterogeneity, low-temperature atmospheric processes altering the observed abundances, or systematic shortcomings in the models. We computed the present-day local luminosity and mass functions of the two clusters; our data reveal a strong flattening of the mass function indicative of a significant preferential loss of low-mass stars in agreement with previous dynamical models for these two clusters. We made our NIRISS astro-photometric catalogs and stacked images publicly available to the community. Description: Astro-photometric catalogs and stakced images of NGC 6121 and NGC 6397. Caveats about the catalogs and their usage can be found in Appendix C of the paper. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file ngc6121.dat 280 12270 ngc6397.dat 204 11566 stacks/* . 2 *Astrometrized stacked images -------------------------------------------------------------------------------- Note on stacks/*: The directory contains the astrometrized stacked images obtained with the JWST/NIRISS data -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- Byte-by-byte Description of file: ngc6121.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 14 F14.10 --- ra Right Ascension (ICRS) at epoch 2023 16- 29 F14.10 --- dec Declination (ICRS) at epoch 2023 31- 39 F9.4 --- x x master-frame position (40 mas/pixel) 41- 50 F10.4 --- y y master-frame position (40 mas/pixel) 52- 56 I5 --- nstar ID number of the source 58- 64 F7.4 --- m1501c Calibrated JWST/NIRISS F150W magnitude 66- 72 F7.4 --- m606c Calibrated JWST/ACS/WFC F606W magnitude 74- 80 F7.4 --- m814c Calibrated JWST/ACS/WFC F814W magnitude 82- 82 I1 --- field_flag Field flag (1) 84- 84 I1 --- membership Membership flag (2) 86- 86 I1 --- sat150 F150W saturation flag (3) 88- 95 F8.4 --- m150 F150W instrumental magnitude 97-103 F7.4 --- sm150 F150W magnitude rms 105-109 F5.3 --- q150 F150W quality-of-PSF-fit parameter 111-119 F9.4 --- o150 F150W fractional flux due to neighbors within the fitting radius prior to neighbor subtraction 121-122 I2 --- f150 Number of individual F150W exposures in which an object was found 124-125 I2 --- g150 Number of individual F150W exposures used to measure an object 127-134 F8.4 --- rxs150 F150W excess/deficiency of flux outside the fitting radius (RADXS) 136-142 F7.2 --- sky150 F150W sky in DN 144-150 F7.2 --- rmssky150 F150W sky rms in DN 152-152 I1 --- sat606 F606W saturation flag (3) 154-161 F8.4 --- m606 F606W instrumental magnitude 163-169 F7.4 --- sm606 F606W magnitude rms 171-175 F5.3 --- q606 F606W quality-of-PSF-fit parameter 177-183 F7.4 --- o606 F606W fractional flux due to neighbors within the fitting radius prior to neighbor subtraction 185-186 I2 --- f606 Number of individual F606W exposures in which an object was found 188-189 I2 --- g606 Number of individual F606W exposures used to measure an object 191-198 F8.4 --- rxs606 F606W excess/deficiency of flux outside the fitting radius (RADXS) 200-206 F7.2 --- sky606 F606W sky in electrons 208-214 F7.2 --- rmssky606 F606W sky in electrons 216-216 I1 --- sat814 F814W saturation flag (3) 218-225 F8.4 --- m814 F814W instrumental magnitude 227-233 F7.4 --- sm814 F814W magnitude rms 235-239 F5.3 --- q814 F814W quality-of-PSF-fit parameter 241-248 F8.4 --- o814 F814W fractional flux due to neighbors within the fitting radius prior to neighbor subtraction 250-251 I2 --- f814 Number of individual F814W exposures in which an object was found 253-254 I2 --- g814 Number of individual F814W exposures used to measure an object 256-263 F8.4 --- rxs814 F814W excess/deficiency of flux outside the fitting radius (RADXS) 265-271 F7.2 --- sky814 F814W sky in electrons 273-279 F7.2 --- rmssky814 F814W sky in electrons -------------------------------------------------------------------------------- Note (1): The JWST/NIRISS Norther field has a field_flag of 1, while the Southern field has a field_flag of 2 Note (2): Cluster stars have membership=1, all other objects have membership=0 Note (3): Saturated stars have a saturation flag set to 9. If multiple exposure times are present in the data set, the saturation flag is 0 for a measurement obtained from the longest exposure(s), and progressively increases (by 1) with decreasing exposure time of the image(s) from which it was measured -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- Byte-by-byte Description of file: ngc6397.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 14 F14.10 --- ra Right Ascension (ICRS) at epoch 2023 16- 29 F14.10 --- dec Declination (ICRS) at epoch 2023 31- 39 F9.4 --- x x master-frame position (40 mas/pixel) 41- 49 F9.4 --- y y master-frame position (40 mas/pixel) 51- 55 I5 --- nstar ID number of the source 57- 63 F7.4 --- m150c Calibrated JWST/NIRISS F150W magnitude 65- 71 F7.4 --- m775c Calibrated JWST/ACS/WFC F775W magnitude 73- 73 I1 --- membership Membership flag (1) 75- 75 I1 --- sat150 F150W saturation flag (2) 77- 84 F8.4 --- m150 F150W instrumental magnitude 86- 92 F7.4 --- sm150 F150W magnitude rms 94- 98 F5.3 --- q150 F150W quality-of-PSF-fit parameter 100-109 F10.4 --- o150 F150W fractional flux due to neighbors within the fitting radius prior to neighbor subtraction 111-112 I2 --- f150 Number of individual F150W exposures in which an object was found 114-115 I2 --- g150 Number of individual F150W exposures used to measure an object 117-124 F8.4 --- rxs150 F150W excess/deficiency of flux outside the fitting radius (RADXS) 126-132 F7.2 --- sky150 F150W sky in DN 134-140 F7.2 --- rmssky150 F150W sky rms in DN 142-142 I1 --- sat775 F150W saturation flag (2) 144-151 F8.4 --- m775 F775W instrumental magnitude 153-159 F7.4 --- sm775 F775W magnitude rms 161-165 F5.3 --- q775 F775W quality-of-PSF-fit parameter 167-174 F8.4 --- o775 F775W fractional flux due to neighbors within the fitting radius prior to neighbor subtraction 176-176 I1 --- f775 Number of individual F775W exposures in which an object was found 178-178 I1 --- g775 Number of individual F775W exposures used to measure an object 180-187 F8.4 --- rxs775 F775W excess/deficiency of flux outside the fitting radius (RADXS) 189-195 F7.2 --- sky775 F775W sky in electrons 197-203 F7.2 --- rmssky775 F775W sky rms in electrons -------------------------------------------------------------------------------- Note (1): Cluster stars have membership=1, all other objects have membership=0 Note (2): Saturated stars have a saturation flag set to 9. If multiple exposure times are present in the data set, the saturation flag is 0 for a measurement obtained from the longest exposure(s), and progressively increases (by 1) with decreasing exposure time of the image(s) from which it was measured -------------------------------------------------------------------------------- Acknowledgements: Mattia Libralato References: Libralato et al. (2024) JWST Imaging of the Closest Globular Clusters--IV. Chemistry, luminosity and mass functions of the lowest-mass members in the NIRISS parallel fields