The 19th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun Edited by G. A. Feiden THE UBVRI AND INFRARED COLOUR INDICES OF THE SUN AND SUN-LIKE STARS Mehmet TANRIVER1, Ferhat Fikri ÖZEREN1 1 Erciyes University, Astronomy and Space Sciences Department, 38039, Kayseri, Turkey Abstract The Sun is not a point source, the photometric observational techniques that are utilised for observing other stars cannot be utilised for the Sun, meaning that it is diﬃcult to derive its colours accurately for astronomical work from direct measurements in diﬀerent passbands. The solar twins are the best choices because they are the stars that are ideally the same as the Sun in all parameters, and also, their colours are highly similar to those of the Sun. From the 60 articles on the Sun and Sun-like stars in the literature from 1964 until today, the solar colour indices in the optic and infrared regions have been estimated. 1 INTRODUCTION The Sun is an average-low-mass star in the main sequence of the Hertzsprung-Russell diagram. Moreover, the Sun is not a point source, the photometric observational techniques that are utilised for observing other stars cannot be utilised for the Sun. Therefore, the colours and colour indices of the sun-like stars are used in order to determine the sun’s colour indices. These stars generally become the solar analog stars. The highlighted results of the important researches in the literature were collected 8240 records with the colour indices data of the Sun, solar analog, and solar twin stars. 2 THE ESTIMATION of THE SOLAR COLOUR INDICES The aim is to determine the sun’s colour indices and to cre- ate the ASAS catalogue (Pojmanski, 1997) (Paczyński et al., 2006) of the sun-like stars. It is taking the average of the colours and colour indices of the solar twin stars having the same spectral type with the sun. So, it is that the sun’s colour indices were determined indirectly. In this study, we have collected the colour indices of solar analog and solar twin stars in the literature. By averaging of these, we have in- directly estimated the colour indices of the sun ( Tanrıver (2012), Tanrıver (2014a), Tanrıver (2014b) ). For this, it is used the data given in the literature records (8240) Then, we have listed sun-like stars in the ASAS catalogue. These values are given in Table1 as follows. One of the Sun like system is HT Vir multiple system (Tanrıver & Özeren, 2016) . The range of colours valid for the solar analog and solar twin stars can also be seen in Figures 1 and 2. 3 THE SOLAR ANALOG nad SOLAR TWIN STARS in THE ASAS CATALOGUE The Sun-like stars in the ASAS catalogue are determined by using the obtained ranges of colour for the solar analog and solar twin stars ( Tanrıver (2012), Tanrıver (2014a), Tan- rıver (2014b) ). The table of the Sun-like variable stars in the ASAS catalogue is given as follows a portion of the table with Table 1: The obtained average colour indices values of the Sun with standart deviation (±σ)( Tanrıver (2012), Tanrıver (2014a), Tanrıver (2014b) ). B-V 0.6457 ± 0.0421 V-J 1.1413 ± 0.1063 H-K 0.0572 ± 0.0351 U-B 0.1463 ± 0.0596 V-H 1.4613 ± 0.1183 J-K 0.3777 ± 0.0494 R-I 0.3403 ± 0.0356 V-K 1.5210 ± 0.1149 J-L 0.4187 ± 0.0558 U-V 0.7926 ± 0.1032 V-L 1.5167 ± 0.0959 J-M 0.3711 ± 0.0529 V-R 0.4674 ± 0.0639 V-M 1.4621 ± 0.0759 K-L 0.0403 ± 0.0517 V-I 0.7053 ± 0.0872 J-H 0.3196 ± 0.0432 K-M 0.0063 ± 0.0546 3764 records. 4 CONCLUSION and DISCUSSION There are many studies in the literature concerning solar twin stars, such as 18 Sco, HIP 78399 and HD 98618. There are solar twin candidates suggested in the literature to be highly similar to the Sun, too. The other stars demonstrating con- sistency with our results from among solar twin stars in the literature are given in Table5 as follows. It can be asserted that these stars in our Sun-like ASAS list are the best solar twin stars, which are photometrically similar to the Sun ac- cording to our research. Simultaneously, there