The Optical to Infrared Extinction Law of Magellanic Clouds Based on Red Supergiant and Classical Cepheid

Precise interstellar dust extinction laws are important to infer the intrinsic properties of reddened objects and correctly interpret observations. In this work, we attempt to measure the optical--infrared extinction laws of the Large and Small Magellanic Clouds (LMC and SMC) by using red supergiant (RSG) stars and classical Cepheids as extinction tracers. The spectroscopic RSG samples are constructed based on the APOGEE spectral parameters, Gaia astrometric data, and multi-band photometry. We establish the effective temperature--intrinsic color relations for RSG stars and determine the color excess ratio (CER) E(lambda-GRP)/E(GBP-GRP) for LMC and SMC. We use classical Cepheids to derive base relative extinction A_GRP/E(GBP-GRP). The results are 1.589+-0.014 and 1.412+-0.041 for LMC and SMC. By combining CERs with A_GRP /E(GBP-GRP), the optical--infrared extinction coefficients A_lambda/A_GRP are determined for 16 bands. We adjust the parameters of Rv-dependent extinction laws and obtain the average extinction law of LMC and SMC as Rv=3.40+-0.07 and Rv=2.53+-0.10, which are consistent with Gordon et al. (2003). In the optical bands, the adjusted Rv extinction curves agree with the observations with deviations less than 3%.Comment: 24 pages, 12 figures, 6 tables, Accepted for publication in Ap

Distances to the Supernova Remnants in the Inner Disk

Distance measurements of supernova remnants (SNRs) are essential and important. Accurate estimates of physical size, dust masses, and some other properties of SNRs depend critically on accurate distance measurements. However, the determination of SNR distances is still a tough task. Red clump stars (RCs) have a long history been used as standard candles. In this work, we take RCs as tracers to determine the distances to a large group of SNRs in the inner disk. We first select RC stars based on the near-infrared (IR) color-magnitude diagram (CMD). Then, the distance to and extinction of RC stars are calculated. To extend the measurable range of distance, we combine near-IR photometric data from the 2MASS survey with the deeper UKIDSS and VVV surveys. With the help of the Gaia parallaxes, we also remove contaminants including dwarfs and giants. Because an SN explosion compresses the surrounding interstellar medium, the SNR region would become denser and exhibit higher extinction than the surroundings. The distance of a SNR is then recognized by the position where the extinction and its gradient is higher than that of the ambient medium. A total of 63 SNRs' distances in the Galactic inner disk are determined and divided into three Levels A, B, and C with decreasing reliability. The distances to 43 SNRs are well determined with reliability A or B. The diameters and dust masses of SNRs are estimated with the obtained distance and extinction.Comment: 31 pages, 25 figures, 2 tables, accepted for publication in A&

A search for open cluster Cepheids in the Galactic plane

We analyse all potential combinations of Galactic Cepheids and open clusters (OCs) in the most up-to-date catalogues available. Isochrone fitting and proper-motion calcula- tion are applied to all potential OC{Cepheid combinations. Five selection criteria are used to select possible OC Cepheids: (i) the Cepheid of interest must be located within 60 arcmin of the OC's centre; (ii) the Cepheid's proper motion is located within the 1 sigma distribution of that of its host OC; (iii) the Cepheid is located in the instability strip of its postulated host OC; (iv) the Cepheid and OC distance moduli should differ by less than 1 mag; and (v) the Cepheid and OC ages (and, where available, their metal- licities) should be comparable: {\Delta}log(t yr^-1) < 0.3. Nineteen possible OC Cepheids are found based on our near-infrared (NIR) analysis; eight additional OC{Cepheid associations may be genuine pairs for which we lack NIR data. Six of the Cepheids analysed at NIR wavelengths are new, high-probability OC Cepheids, since they lie on the near-infrared (NIR) period (P){luminosity relation (PLR). These objects include TY Sct and CN Sct in Dolidze 34, XX Sgr in Dolidze 52, CK Sct in NGC 6683, VY Car in ASCC 61 and U Car in Feinstein 1. Two additional new OC Cepheids lack NIR data: V0520 Cyg in NGC 6991 and CS Mon in Juchert 18. The NIR PLR for our confirmed sample of OC Cepheids is M_J = (-3.12 +/- 0.29) log(P day^-1)-(2.17 +/- 0.29) mag, which is in good agreement with the best NIR PLR available for all Galactic Cepheids.Comment: 16 pages, 11 figures, 3 tables; accepted for publication in MNRA

Double Mode Cepheids from the Zwicky Transient Facility Survey

Multi-mode Cepheids pulsate simultaneously in more than one mode of oscillation. They provide an independent means to test stellar models and pulsation theories. They can also be used to derive metallicities. In recent years, the number of known multi-mode Cepheids has increased dramatically with the discovery of a large number of Galactic double-mode Cepheids. To date, 209 double-mode Cepheids have been detected in the Galactic bulge and disk, mostly based on the Optical Gravitational Lensing Experiment's (OGLE) catalog. In this paper, we conduct a comprehensive search for double-mode Cepheids in the northern sky based on Zwicky Transient Facility Data Release 5. We found 72 such objects in the Milky Way. The periods of the 30 sample objects already included in the OGLE catalog show excellent agreement with the OGLE periods. The period ratios of our new Cepheids are consistent with those of known double-mode Cepheids, as evidenced by their loci in the so-called `Petersen diagram'. Compared with OGLE, the completeness of our double-mode Cepheid sample is around 71\%. The much improved temporal sampling of the Zwicky Transient Facility offers significant scope to find more double-mode Cepheids, especially at the distribution's short-period end.Comment: 11 pages, 3 figures, 3 tables; accepted for publication in ApJ

Unravelling the Period Gap using LAMOST Chromospheric Activity Indices

In our recent catalogue of BY Draconis (BY Dra) variables based on Zwicky Transient Facility data, we found traces of a period gap in the period-colour diagram. We combined our BY Dra database with catalogues from the {\sl Kepler} and K2 surveys, revealing a prominent period gap. Here, we use this combined ZTF-{\sl Kepler}-K2 data set to investigate the origin of the period gap observed for BY Dra stars using chromospheric activity indices. We use low- and medium-resolution spectra from the LAMOST Data Release 7 to derive magnetic activity indices for the Ca {\sc ii} H and K and H$\alpha$ emission lines. We find a strong dependence of chromospheric activity on both stellar mass and rotation period. For partially convective K-M-type stars, the activity decreases steeply up to an age of $\sim$700-1000 Myr, subsequently evolving to the type of low-level saturation associated with spin-down stallation. In contrast, F-G-type stars with thinner convective envelopes exhibit constant activity with increasing age. We suspect that the observed steep decrease for partially convective stars is driven by core-envelope coupling. This mechanism reduces differential rotation at the core-envelope transition, hence leading to decreased magnetic activity. Moreover, we derive activity indices for previously known star clusters and find similar trends as regards their activity levels as a function of age. In particular, very low-level activity is observed around the location of the period gap. Therefore, we conclude that the period gap, defined by the non-detection of variable sources, is driven by a minimum in chromospheric activity