We investigate infrared properties of OGLE4 Mira variables in our Galaxy. For each object, we cross-identify the AllWISE, 2MASS, Gaia, and IRAS counterparts. We present various IR two-color diagrams (2CDs) and period-magnitude and period-color relations for the Mira variables. Generally, the Mira variables with longer periods are brighter in the IR fluxes and redder in the IR colors. In this work, we also revise and update the previous catalog of AGB stars in our Galaxy using the new sample of OGLE4 Mira variables. Now, we present a new catalog of 74,093 (64,609 O-rich and 9,484 C-rich) AGB stars in our Galaxy. A group of 23,314 (19,196 O-rich and 4,118 C-rich) AGB stars are identified based on the IRAS PSC and another group of 50,779 (45,413 O-rich and 5,366 C-rich) AGB stars are identified based on the AllWISE source catalog. For all of the AGB stars, we cross-identify the IRAS, AKARI, MSX, AllWISE, 2MASS, OGLE4, Gaia, and AAVSO counterparts and present various infrared 2CDs. Comparing the observations with the theory, we find that basic theoretical dust shell models can account for the IR observations fairly well for most of the AGB stars.

We present various infrared two-color diagrams (2CDs) using WISE data for asymptotic giant branch (AGB) stars and Planetary Nebulae (PNe) and investigate possible evolutionary tracks. We use the sample of 5036 AGB stars, 660 post-AGB stars, and 2748 PNe in our Galaxy. For each object, we cross-identify the IRAS, AKARI, WISE, and 2MASS counterparts. To investigate the spectral evolution from AGB stars to PNe, we compare the theoretical model tracks of AGB stars and post-AGB stars with the observations on the IR 2CDs. We find that the theoretical dust shell model tracks can roughly explain the observations of AGB stars, post-AGB stars, and PNe on the various IR 2CDs. WISE data are useful in studying the evolution of AGB stars and PNe, especially for dim objects. We find that most observed color indices generally increase during the evolution from AGB stars to PNe. We also find that Fe0.9Mg0.1O dust is useful to fit the observed WISE W3-W4 colors for O-rich AGB stars with thin dust shells.

We present a new catalog of AGB stars based on infrared two-color diagrams (2CDs) and known properties of the pulsations and spectra. We exclude some misclassified objects from previous catalogs. We identify color areas in two IR 2CDs where most O-rich and C-rich objects listed in previous catalogs of AGB stars are found. By collecting new objects in these color selection areas in the two IR 2CDs, we find candidate objects for AGB stars. By using the color selection method, we identify 3996 new objects in the O-rich areas, 1487 new objects in the C-rich areas, and 295 new objects in the overlap areas of the two 2CDs simultaneously. We have found that 470 O-rich and 9 C-rich objects are Mira variables with positive spectral identification and they are newly identified AGB stars. We present a new catalog of 3828 O-rich AGB stars and 1168 C-rich AGB stars excluding misclassified objects and adding newly identified objects.

We investigate optical properties of amorphous alumina (Al2O3) dust grains in the envelopes around O-rich asymptotic giant branch (AGB) stars using laboratory measured optical data. We derive the optical constants of amorphous alumina over a wide wavelength range that satisfy the Kramers- Kronig relation and reproduce the laboratory data. Using the amorphous alumina and silicate dust, we compare the radiative transfer model results with the observed spectral energy distributions. Comparing the theoretical models with observations on various IR two-color diagrams for a large sample of O-rich AGB stars, we find that the amorphous alumina dust (about 10-40%) mixed with amorphous silicate better models the observed points for the O-rich AGB stars with thin dust envelopes.

The main site of dust formation is believed to be the cool envelopes around AGB stars. Nearly all AGB stars can be identified as long-period variables (LPVs) with large amplitude pulsation. Shock waves produce by the strong pulsation and radiation pressure on newly formed dust grains drive dusty stellar winds with high mass-loss rates. IR observations of AGB stars identify various dust species in different physical conditions. Radio observations of gas phase materials are helpful to understand the overall properties of the stellar winds. In this paper, we review (i) classification of AGB stars; (ii) IR two-color diagrams of AGB stars; (iii) pulsation of AGB stars; (iv) dust around AGB stars including dusty stellar winds; (v) dust envelopes around AGB stars; (vi) mass-loss and evolution of AGB stars; and (vii) contribution of AGB dust to galactic environments. We discuss various observational evidences and their theoretical interpretations.

We model dust around Herbig Ae/Be stars using a radiative transfer model for multiple isothermal circumstellar dust shells to reproduce the multiple broad peaks in their spectral energy distributions (SEDs). Using the opacity functions for various types of dust grains at different temperatures, we calculate the radiative transfer model SEDs for multiple dust shells. For eight sample stars, we compare the model results with the observed SEDs including the Infrared Space Observatory (ISO) and AKARI data. We present model parameters for the best fit model SEDs that would be helpful to understand the overall structure of dust envelopes around Herbig Ae/Be stars. We find that at least four separate dust components are required to reproduce the observed SEDs. For all the sample stars, two innermost dust components (a hot component of 1000-1500 K and a warm component of 300-600 K) with amorphous silicate and carbon grains are needed. Crystalline dust grains (corundum, forsterite, olivine, and water ice) are needed for some objects. Some crystalline dust grains exist in cold regions as well as in hot inner shells.

In order to study properties of the pulsation in the infrared emission for long period variables, we collect and analyze the infrared observational data at L band for 12 OH/IR. The observation data cover about three decades including recent data from the ISO and Spitzer. We use the Marquardt-Levenberg algorithm to determine the pulsation period and amplitude for each star and compare them with results of previous investigations at infrared and radio bands. We obtain the relationship between the pulsation periods and the amplitudes at L band. Contrary to the results at K band, there is no difference of the trends in the short and long period regions of the period-luminosity relation at L band. This may be due to the molecular absorption effect at K band. The correlations among the L band parameters, IRAS [12-25] colors, and K band parameters may be explained as results of the dust shell parameters affected by the stellar pulsation. The large scatter of the correlation could be due to the existence of a distribution of central stars with various masses and pulsation modes.

We make a new catalog of AGB stars in our Galaxy from the sources listed in the Infrared Astronomical Satellite (IRAS) point source catalog (PSC) compiling the lists of previous works with verifying processes. We verify the class identification of AGB stars into oxygen-rich and carbon-rich stars using the information from recent investigations. For the large sample of AGB stars, we present infrared two-color diagrams from the observations at near infrared bands and IRAS PSC. On the two-color diagrams, we plot the tracks of theoretical radiative transfer model results with increasing dust shell optical depths. Comparing the observations with the theoretical tracks, we discuss the meaning of the infrared two-color diagrams.

We investigate the spectral energy distributions (SEDs) of low mass-loss rate O-rich asymptotic giant branch (AGB) stars using the infrared observational data including the Infrared Space Observatory (ISO) data. Comparing the results of detailed radiative transfer model calculations with observations, we find that the dust formation temperature is much lower than 1000 K for standard dust shell models. We find that the superwind model with a density-enhanced region can be a possible alternative dust shell model for LMOA stars.