RR Lyrae variables in the globular cluster M3 (NGC5272). I. BVI CCD photometry

New BVI CCD photometry is presented for 60 RR Lyrae variables in the globular cluster M3. Light curves have been constructed and ephemerides have been (re)-derived for all of them. Four stars (i.e. V29, V136, V155 and V209), although recognized as variables, had no previous period determinations. Also, the period derived for V129 is significantly different from the one published by Sawyer-Hogg (1973). Light curve parameters, i.e. mean magnitudes, amplitudes and rise-times, have been derived. The discussion of these results in the framework of the stellar evolution and pulsation theories will be presented in a forthcoming paper.Comment: 19 pages, latex, uses mn.sty, 12 encapsulated figures, to be published in MNRAS, text and figures also available at http://www.bo.astro.it/bap/BAPhome.html or via anonymous ftp at ftp://boas3.bo.astro.it/bap/files (bap98-12-textfig.ps

The Gaia spectrophotometric standard stars survey - III. Short-term variability monitoring

We present the results of the short-term constancy monitoring of candidate Gaia Spectrophotometric Standard Stars (SPSS). We obtained time series of typically 1.24 h - with sampling periods from 1-3 min to a few hours, depending on the case - to monitor the constancy of our candidate SPSS down to 10 mmag, as required for the calibration of Gaia photometric data. We monitored 162 out of a total of 212 SPSS candidates. The observing campaign started in 2006 and finished in 2015, using 143 observing nights on nine different instruments covering both hemispheres. Using differential photometry techniques, we built light curves with a typical precision of 4 mmag, depending on the data quality. As a result of our constancy assessment, 150 SPSS candidates were validated against short-term variability, and only 12 were rejected because of variability including some widely used flux standards such as BD+174708, SA 105-448, 1740346, and HD 37725

The Gaia spectrophotometric standard stars survey - V. Preliminary flux tables for the calibration of Gaia DR2 and (E)DR3

We present the flux tables of the spectrophotometric standard stars (SPSS) used to calibrate in flux the Gaia DR2 and (E)DR3 data releases. The latest SPSS grid version contains 112 stars, whose flux tables agree to better than 1 per cent with the CALSPEC spectra of 11 flux standards for the calibration of the Hubble Space Telescope. The synthetic magnitudes computed on the SPSS spectra also agree to better than 1 per cent with the Landolt magnitudes of 37 stars in common. The typical spreads in both comparisons are of the order of 1 per cent. These uncertainties already meet the initial requirements for the Gaia SPSS project, but further improvements are expected in the next SPSS versions, that will be used to calibrate future Gaia releases. We complement the SPSS flux tables with literature spectra of 60 additional stars that did not pass all the criteria to be SPSS, the Passband Validation Library (PVL). The PVL contains stars of extreme spectral types, such as bright O and B stars and late M stars and brown dwarfs, and was useful to investigate systematic effects in the previous Gaia DR2 release and to minimize them in the EDR3 one. The PVL literature spectra are recalibrated as accurately as possible on to the SPSS reference scale, so that the two sets together can be used in a variety of validation and comparison studie

The Gaia spectrophotometric standard stars survey - IV. Results of the absolute photometry campaign

We present Johnson-Kron-Cousins BVRI photometry of 228 candidate spectrophotometric standard stars for the external (absolute) flux calibration of Gaia data. The data were gathered as part of a 10-yr observing campaign with the goal of building the external grid of flux standards for Gaia and we obtained absolute photometry, relative photometry for constancy monitoring, and spectrophotometry. Preliminary releases of the flux tables were used to calibrate the first two Gaia releases. This paper focuses on the imaging frames observed in good sky conditions (about 9100). The photometry will be used to validate the ground-based flux tables of the Gaia spectrophotometric standard stars and to correct the spectra obtained in non-perfectly photometric observing conditions for small zero-point variations. The absolute photometry presented here is tied to the Landolt standard stars system to ≃1 per cent or better, depending on the photometric band. Extensive comparisons with various literature sources show an overall ≃1 per cent agreement, which appears to be the current limit in the accuracy of flux calibrations across various samples and techniques in the literature. The Gaia photometric precision is presently of the order of 0.1 per cent or better, thus various ideas for the improvement of photometric calibration accuracy are discussed.This work was supported by the MINECO (Spanish Ministry of Economy and Competitiveness) through grant RTI2018-095076-B-C21 (MINECO/FEDER- Fondo Europeo de Desarrollo Regional, UE). APV acknowledges FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo) for the postdoctoral fellowship No. 2017/15893-1 and the DGAPA (Dirección General de Asuntos del Personal Académico) PAPIIT grant IG100319

The Gaia spectrophotometric standard stars survey - III. Short-term variability monitoring

We present the results of the short-term constancy monitoring of candidate Gaia Spectrophotometric Standard Stars (SPSS). We obtained time series of typically 1.24 h - with sampling periods from 1-3 min to a few hours, depending on the case - to monitor the constancy of our candidate SPSS down to 10 mmag, as required for the calibration of Gaia photometric data. We monitored 162 out of a total of 212 SPSS candidates. The observing campaign started in 2006 and finished in 2015, using 143 observing nights on nine different instruments covering both hemispheres. Using differential photometry techniques, we built light curves with a typical precision of 4 mmag, depending on the data quality. As a result of our constancy assessment, 150 SPSS candidates were validated against short-term variability, and only 12 were rejected because of variability including some widely used flux standards such as BD+174708, SA 105-448, 1740346, and HD 37725

GRB100816A: TNG optical afterglow confirmation.

We observed the field of the short hard GRB100816A (Swift trigger 431764; Oates et al., GCN 11102) with the Italian 3.6m TNG telescope (La Palma, Canary Islands) equipped with the DOLORES camera. Observations started on Aug 16 at 03:22 UT (~2.8 hrs after the burst) under very poor weather conditions (high cloudiness and high humidity). We acquired a R band image of the GRB field for a total exposure time of 180s. We clearly detect a source consistent with the one reported by (Oates et al., GCN 11102). This souce, located at RA (J2000)=23:26:57.58; Dec(J2000)=+26:34:42.7 (+/-0.5''), showed a magnitude R~20.5 (calibrated against USNO B1.0) at the epoch of the observation. Due to its fading behavior with respect to the UVOT observation, we confirm that this source is the optical afterglow of GRB100816A