3D maps of the local ISM from inversion of individual color excess measurements

Inversion of interstellar (IS) gas or dust absorbing columns measured along the path to stars distributed in distance and direction allows reconstructing the distribution of interstellar matter (ISM) in three dimensions. A low resolution IS dust map based on reddening measurements towards 23,000 nearby stars is used to illustrate the potential of the more detailed maps that are expected within the next several years. The map reveals the location of the main IS cloud complexes up to distances on the order of 600 to 1200 pc depending on directions. Owing to target selection biases towards weakly reddened, brighter stars, the map is especially revealing in terms of regions devoid of IS matter. It traces the Local Bubble and its neighboring cavities, including a conspicuous, giant, ≥1000 pc long cavity in the third quadrant located beyond the so-called βMa tunnel. This cavity is bordered by the main constituents of the Gould belt, the well-known and still unexplained rotating and expanding ring of clouds and young stars, inclined by ~ 20° to the galactic plane. Comparing the dust distribution with X-ray emission maps and IS gas observations shows that the giant cavity contains a large fraction of warm, fully ionized and dust-poor gas in addition to million K, X-ray bright gas. This set of structures must reflect the main events that occurred in the past; today however even the formation of the Gould belt is still a matter of controversy.It has been suggested recently that the Cretaceus-Tertiary (KT) mass extinction is potentially due to a gamma-ray burst (GRB) that occurred in the massive globular cluster (GC) 47 Tuc during its close encounter with the Sun ~70 Myrs ago. Such a hypothesis is based on computations of the cluster and Sun trajectories and the frequency of short GRBs in GC's. Given the mass, speed and size of 47 Tuc, wherever it crossed the Galactic plane it must have produced at the crossing site significant dynamical effects on the disk stars and IS clouds, and triggered star formation. On the other hand, a burst must have produced huge ionization and radiation pressure effects on the ISM. Therefore, identifying (or not) the corresponding imprints should provide additional clues to the extinction source and the ISM history. Interestingly, first-order estimates suggest that the Gould belt dynamics and age could match the expected consequences of the cluster crossing, and that the giant ionized, dust-free cavity could be related to gas ionization and dust evaporation by an intense flux of hard radiation such as produced by a GRB. Moreover, dust-gas decoupling during the crossing and after the burst could have produce a highly inhomogeneous dust to gas ratio, potentially explaining the high variability and pattern of the D/H ratio in the gas phase. Future Gaia data should confirm or dismiss this hypothesis.

In this study, we present CCD UBV photometry of poorly studied open star clusters, Dolidze 36, NGC 6728, NGC 6800, NGC 7209, and Platais 1, located in the first and second Galactic quadrants. Observations were obtained with T100, the 1-m telescope of the TUBITAK National Observatory. Using photometric data, we determined several astrophysical parameters such as reddening, distance, metallicity and ages and from them, initial mass functions, integrated magnitudes and colours. We took into account the proper motions of the observed stars to calculate the membership probabilities. The colour excesses and metallicities were determined independently using two-colour diagrams. After obtaining the colour excesses of the clusters Dolidze 36, NGC 6728, NGC 6800, NGC 7209, and Platais 1 as $0.19\pm0.06$, $0.15\pm0.05$, $0.32\pm0.05$, $0.12\pm0.04$, and $0.43\pm0.06$ mag, respectively, the metallicities are found to be $0.00\pm0.09$, $0.02\pm0.11$, $0.03\pm0.07$, $0.01\pm0.08$, and $0.01\pm0.08$ dex, respectively. Furthermore, using these parameters, distance moduli and age of the clusters were also calculated from colour-magnitude diagrams simultaneously using PARSEC theoretical models. The distances to the clusters Dolidze 36, NGC 6728, NGC 6800, NGC 7209, and Platais 1 are $1050\pm90$, $1610\pm190$, $1210\pm150$, $1060\pm 90$, and $1710\pm250$ pc, respectively, while corresponding ages are $400\pm100$, $750\pm150$, $400\pm100$, $600\pm100$, and $175\pm50$ Myr, respectively. Our results are compatible with those found in previous studies. The mass function of each cluster is derived. The slopes of the mass functions of the open clusters range from 1.31 to 1.58, which are in agreement with Salpeter's initial mass function. We also found integrated absolute magnitudes varying from -4.08 to -3.40 for the clusters.

The extinction law and the variation of colour excess with position, luminosity and spectral class in young open star clusters NGC 663, NGC 869, NGC 884, NGC 1502, NGC 1893, NGC 2244, NGC 2264, NGC 6611, Tr 14, Tr 15, Tr 16, Coll 228, Tr 37 and Be 86 have been studied. The difference in the minimum and maximum values of of cluster members has been considered as a measure of the presence of non-uniform gas and dust inside the clusters. Its value ranges from 0.22 to 1.03 mag in the clusters under study, which indicates that non-uniform extinction is present in all the clusters. It has been noticed for the first time in NGC 1502 and Tr 37. It is also found that the differential colour excess in open clusters, which may be caused by the presence of gas and dust, decreases systematically with the age of clusters, indicating that matter is either used in star formation or blown away by hot stars or both. There is no uniformity in the variation of with position or spectral class or luminosity. Except in Tr 14, all clusters show a random spatial distribution of , indicating a random distribution of gas and dust inside the clusters. The value correlates with both luminosity and spectral class only in the case of Coll 228, Tr 16 and Be 86. The members of these clusters at show larger values of colour excess ratios than the normal ones. The value of for most of the cluster members is close to the normal interstellar value of 1.73. However, the colour excess ratios with ) at are smaller than the normal value for NGC 663, NGC 869, NGC 884 and NGC 1502, while they are larger for NGC 6611, Coll 228, Tr 16 and Tr 14. Thus there is no uniformity in the relationship of extinction properties amongst the clusters under study.

CCD UBV and Gaia DR3 based analysis of NGC 189, NGC 1758 and NGC 7762 open clusters

We present the BVR broad-band polarimetric observations of 51 stars belonging to the young open cluster IC 1805. Along with the photometric data from the literature, we have modelled and subtracted the foreground dust contribution from the maximum polarization (Pmax) and colour excess [E (B−V)]. The mean value of the Pmax for intracluster medium and the foreground are found to be 5.008 ± 0.005 and 4.865 ± 0.022 per cent, respectively. Moreover, the mean value of the wavelength of maximum polarization (λmax) for intracluster medium is 0.541 ± 0.003 μ m, which is quite similar as the general interstellar medium (ISM). The resulting intracluster dust component is found to have negligible polarization efficiency as compared to interstellar dust. Some of the observed stars in IC 1805 have shown the indication of intrinsic polarization in their measurements.

Open clusters (OCs) are common in the Milky Way, but most of them remain undiscovered. There are numerous techniques, including some machine-learning algorithms, available for the exploration of OCs. However, each method has its limitations and therefore, different approaches to discovering OCs hold significant values. We develop a comprehensive approach method to automatically explore the data space and identify potential OC candidates with relatively reliable membership determination. This approach combines the techniques of Hierarchical Density-Based Spatial Clustering of Applications with Noise, Gaussian mixture model, and a novel cluster member identification technique, color excess constraint. The new method exhibits efficiency in detecting OCs while ensuring precise determination of cluster memberships. Because the main feature of this technique is to add an extra constraint (EC) for the members of cluster candidates using the homogeneity of color excess, compared to typical blind search codes, it is called Blind Search-Extra Constraint (BSEC) method. It is successfully applied to the Gaia Data Release 3, and 83 new OCs are found, whose color–magnitude diagrams (CMDs) are fitted well to the isochrones. In addition, this study reports 621 new OC candidates with discernible main sequence or red giant branch. It is shown that BSEC technique can discard some false negatives of previous works, which takes about three percentage of known clusters. It shows that as an EC, the color excess (or two-color) constraint is useful for removing fake cluster member stars from the clusters that are identified from the positions and proper motions of stars, and getting more precise CMDs, when differential reddening of member stars of a cluster is not large (e.g., ΔE(G BP − G RP) < 0.5 mag). It makes the CMDs of 15% clusters clearer (in particular for the region near turnoff) and therefore is helpful for CMD and stellar population studies. Our result suggests that the color excess constraint is more appropriate for clusters with small differential reddening, such as globular clusters or older OCs, and clusters that the distances of member stars cannot be determined accurately.

We analysed the open clusters Czernik 2 and NGC 7654 using CCD UBV photometric and Gaia Early Data Release 3 (EDR3) photometric and astrometric data. Structural parameters of the two clusters were derived, including the physical sizes of Czernik 2 being r=5 and NGC 7654 as 8 min. We calculated membership probabilities of stars based on their proper motion components as released in the Gaia EDR3. To identify member stars of the clusters, we used these membership probabilities taking into account location and the impact of binarity on main-sequence stars. We used membership probabilities higher than $P=0.5$ to identify 28 member stars for Czernik 2 and 369 for NGC 7654. We estimated colour-excesses and metallicities separately using two-colour diagrams to derive homogeneously determined parameters. The derived $E(B-V)$ colour excess is 0.46(0.02) mag for Czernik 2 and 0.57(0.04) mag for NGC 7654. Metallicities were obtained for the first time for both clusters, -0.08(0.02) dex for Czernik 2 and -0.05(0.01) dex for NGC 7654. Keeping the reddening and metallicity as constant quantities, we fitted PARSEC models using colour-magnitude diagrams, resulting in estimated distance moduli and ages of the two clusters. We obtained the distance modulus for Czernik 2 as 12.80(0.07) mag and for NGC 7654 as 13.20(0.16) mag, which coincide with ages of 1.2(0.2) Gyr and 120(20) Myr, respectively. The distances to the clusters were calculated using the Gaia EDR3 trigonometric parallaxes and compared with the literature. We found good agreement between the distances obtained in this study and the literature. Present day mass function slopes for both clusters are comparable with the value of Salpeter (1955), being X=-1.37(0.24) for Czernik 2 and X=-1.39(0.19) for NGC 7654.

With Tycho-2 BT and VT photometry of Hipparcos stars with π 8.0 mas, /π 15% and with spectral type and luminosity classification from the Michigan Catalogues we have a presumably unreddened sample for establishing a ( main sequence relation in the range from A0 to G5. We discuss the location of the median main sequence relation relative to published ZAMS relations for the A0-G5 range in some detail since the applications of this relation will have to assume that the evolutionary status of the calibration sample is representative of the local disk. If the ZAMS is defined as the lower envelope of the class V stars the published versions we discuss seem to be too bright by about half a magnitude in the F0-G5 range. The resulting intrinsic color and absolute magnitude estimates have errors of the mean of 003 and 03–04 respectively. From this relation any given star with Tycho-2 photometry, spectral classification and luminosity class V can have its color excess and distance modulus estimated. This means that the local interstellar extinction may be estimated for the ~50% of the sky where Michigan classification presently is available. The individual color excesses and distance moduli may not be particularly accurate but we propose that they may be used to indicate extinction discontinuities caused by interstellar material at well defined distances. We have applied this new technique on stars from the Michigan Catalogue in the direction of LDN 1622 supposed to be associated to the Orion B region 400–500 pc away but color excesses exceeding start appearing already in the distance slot 160–200 pc. Presently we cannot decide whether this nearby dust is related to LDN 1622 or whether this cloud is associated to Orion B. In a final comparison we study the color excess – distance variation in a 4° region centered on LDN 1622 from Hipparcos – Tycho-1 – Michigan data and the dust at ~160 pc is confirmed.

The interstellar magnetic field (ISMF) near the heliosphere is a basic part of the solar neighborhood that can only be studied using polarized starlight. Results of an ongoing survey of polarized starlight are analyzed with the goal of linking the interstellar magnetic field that shapes the heliosphere to the nearby field in interstellar space. New results for the direction of the nearby ISMF, based on a merit function that utilizes polarization position angles, identify several magnetic components. The dominant interstellar field, B_pol, is aligned with the direction L,B= 36.2,49.0 (+/-16.0) degrees and is within 8 degrees of the IBEX Ribbon ISMF direction. Stars tracing B_pol have the same mean distance as stars that do not trace B_pol, but show weaker polarizations consistent with lower column densities of polarizing grains. The variations in the polarization position angle directions indicate a low level of magnetic turbulence. B_pol is found after excluding polarizations that trace a separate magnetic structure that apparently is due to interstellar dust deflected around the heliosphere. Local interstellar cloud velocities relative to the LSR increase with the angles between the LSR velocities and ISMF, indicating that the kinematics of local interstellar material is ordered by the ISMF. Polarization and color excess data are consistent with an extension of Loop I to the solar vicinity. Polarizations are consistent with previous findings of more efficient grain alignment in low column density sightlines. Optical polarization and color excess data indicate the presence of nearby interstellar dust in the BICEP2 field. Color excess E(B-V) indicates an optical extinction of A_V about 0.59 mag in the BICEP2 field, while the polarization data indicate that A_V is larger than 0.09 mag. The IBEX Ribbon ISMF extends to the boundaries of the BICEP2 region.

Star clusters are crucial for understanding how stars evolve. Their colour–magnitude diagrams show the effects of stellar evolution of approximately coeval objects with the same chemical composition. Furthermore, the determination of their astrophysical parameters (age, distance, colour excess, and metallicity) together with their spatial distribution provides information about the structure and the evolution of the Galaxy itself. Using data from the Gaia DR3 and Two Micron All Sky Survey catalogues, we develop methodologies for characterizing open clusters. Precise membership lists, mean astrometric parameters, and radii are obtained. Using photometric data from both data sources, we carried out new age calibrations that rely on morphological indices based on colour ($\Delta BR$) and magnitude ($\Delta G$) differences between the red clump and the turn-off for a sample of 34 open clusters with ages covering the interval $8.3 &amp;lt; \log [t({\rm yr})] &amp;lt; 9.9$. A set of age calibration functions based on Gaia morphological age indices are determined for the first time. We demonstrate their accuracy, obtaining a mean residual of 0.06 dex in $\log [t({\rm {yr}})]$. Our results also show that stellar evolution models tend to predict the difference $\Delta G$. However, they typically overestimate the difference $\Delta BR$ for objects younger than $\log [t({\rm yr})] = 8.8$.

In this paper, we present our recent work on the evolution of abundance gradients along the Milky Way disk based on the Geneva Copenhagen Survey (GCS) and Radial Velocity Experiment (RAVE) data. We will also discuss the role of the LAMOST Milky Way disk survey in clarifying the properties of metallicity breaks observed through open clusters and young tracers along the Milky Way disk. It is believed that the Galactic disk forms inside-out, in which the stellar population at increasing radii is younger and more metal poor. This picture is consistent with most Galactic Chemical Evolution (GCE) models which also predict a tight correlation between the metallicity and age of stars at a given radius. However, it is only a result of “steady state" and no dynamical evolution effects were taken into account. We have selected two stellar samples from GCS and RAVE, each sample contains about 10,000 local thin-disk, main-sequence stars. We use the guiding radius which is determined by the conservation of z-direction angular momentum, to eliminate the blurring effects. And also use the effective temperature of the main sequence stars as a proxy of stellar age. It is shown that the metallicity gradient flattens as the age increases. This is not consistent with our previous GCE prediction, but can be explained by radial mixing effects. In order to further demonstrate the abundance breaks observed in the Galactic disk we have proposed, and have been carrying out, an open cluster survey project based on LAMOST. We plan to observe at least 400 open clusters in the northern Galactic sky. From the observations, we will get uniform parameters for those clusters with radial velocity and metallicities. We anticipate that this uniform open cluster sample could clarify the observed abundance break around the Milky Way disk corotation radius and also give a more robust result concerning the evolution of the abundance gradient.

view Abstract Citations (48) References (46) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Stars Clusters of the Large Magellanic Cloud: CCD Photometry of NGC 1831 Vallenari, A. ; Chiosi, C. ; Bertelli, G. ; Meylan, G. ; Ortolani, S. Abstract NGC 1831 is a populous, luminous star cluster located in the northern part of the Large Magellanic Cloud. In this paper, we present new Johnson BV-CCD photometry of 1800 stars in the cluster and 300 stars in a nearby field. Particular care is paid to estimate the errors in the data caused by uncertainties in the photometry and by crowding, and to isolate the portion of the cluster suffering from the least degree of incompleteness. The color-magnitude diagram (CMD) shows a well-defined main-sequence band terminating at about V= 18.10, a red giant clump centered at about half of a magnitude below the termination of the main-sequence band and spanning the color range 0.8 <= (B- V)<= 0.9, a sprinkle of stars of the same luminosity but of bluer color scattered toward the main-sequence band, and finally a scarce population of bright red stars. The metallicity, color excess, and distance modulus are derived from literature. The metallicity is assumed to be the mean value from several independent estimates, that is Z = 0.008. The color excess is E_B-V_= 0.05. The adopted distance modulus is (m-M)_0_= 18.5. The CMD and luminosity function (LF) of the main-sequence stars are examined with the aid of two different evolutionary schemes for intermediate mass stars, that is those with the classical extension of the convective regions and those allowing for the occurrence of convective overshoot. With the above metallicity, color excess, and distance modulus, the age of NGC 1831 is about 3.5 x 10^8^ yr with classical models and 5.5 X 10^8^ yr with overshoot models. The analysis of the sole CMD does not allow us to discriminate between the two evolutionary schemes, whereas looking simultaneously at the CMD and LF this is possible. Models with convective overshoot are able to simultaneously fit the morphology of the CMD and the slope of the LF, whereas classical models fail. Finally, the effects of unresolved stars, either true binaries or blended objects, are discussed to some extent. The existence of this type of stars in the CMD and LF does not alter the above conclusions. Publication: The Astronomical Journal Pub Date: September 1992 DOI: 10.1086/116300 Bibcode: 1992AJ....104.1100V Keywords: Astronomical Photometry; Charge Coupled Devices; Color-Magnitude Diagram; Magellanic Clouds; Star Clusters; Stellar Luminosity; Error Analysis; Main Sequence Stars; Stellar Magnitude; Astrophysics; MAGELLANIC CLOUDS; OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NGC 1831 full text sources ADS | data products SIMBAD (2) NED (2)

It is well known that there are few open clusters (OCs) in the high-latitude region of the Milky Way galaxy, because most star formation takes place in the thin disk. It is therefore crucial to look for high Galactic latitude OCs, in order to understand OCs and the Galactic parts outside the plane well. This work looks for high Galactic latitude OCs in Gaia Early Data Release 3, and determines their basic parameters from color–magnitude diagrams (CMDs) if the main sequence is included in CMDs. The friend-of-friend method is applied to the determination of the membership of stars. Star groups with more than 20 bright (G < 18 mag) stars are taken as OC candidates, and these candidates are finally verified by the observed CMDs including stars fainter than 18 mag in the G band. After crossmatching with previous catalogs, 56 new OC candidates are found in the high Galactic latitude region with ∣b∣ ≥ 25°, in which 35 have somewhat clear CMDs and are suggested as newly discovered OCs. Finally, eight of the new OCs are confirmed again by the pyUPMASK technique. The new sample increases the total number of known high Galactic latitude OC candidates significantly. The distance modulus, color excess, metallicity, age, and binary fraction of 35 newly discovered OCs are determined by fitting their observed CMDs to the ASPS stellar population models. All the results are included in the new star cluster catalog, LISC, as its second part (LISC II).

In this paper, a novel approach for the registration method of 3D point cloud maps is presented. During the operation of unmanned system, the construction of 3D maps for the environment is an important prerequisite for many navigation tasks. Generally 3D maps are widely utilized to recognize the location of the unmanned agent. Traditional map aligning techniques that use ICP (Iterative Closest Point) method relate points having the closest distance in different cloud maps in order to combine and extend the 3D maps. The method can be easily adopted in registration among sparse point cloud maps or consecutive scanning problems. However, this approach takes long computation time when aligning large scale maps including a lot of points. Therefore, an improved 3D point cloud map registration method is proposed to register precisely and effectively two maps using low-cost cameras. By combining odometry information derived from the SLAM (Simultaneous Localization and Mapping) procedure and the 3D position of the selected image feature points, location of the coexisting places in both maps are extracted. Then, the estimation of rigid body transform between the origins of each map is achieved. The effectiveness of the presented method is quantitatively validated by experiment on challenging instances of the merging problem and comparison with an existing registration method.

Fil: Orsatti, Ana Maria. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Instituto de Astrofisica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronomicas y Geofisicas. Instituto de Astrofisica la Plata; Argentina