Star Count Data Research Articles

Molecular landscape of canine soft tissue sarcoma

Canine soft tissue sarcomas (STS) are a heterogenous group of malignant tumors arising from mesenchymal cells of soft tissues. This simplified collective of tumors most commonly arise from subcutaneous tissues, are treated similar clinically, and conventionally exclude other sarcomas with more definitive anatomical, histological, or biological features including hemangiosarcoma, lymphangiosarcoma, histiocytic sarcoma, synovial sarcoma, leiomyosarcoma, and rhabdomyosarcoma. Histologically, canine STS sub‐types are difficult to discern at the light microscopic level due to their overlapping microscopic features. Thus, genomic, and transcriptomic profiling of canine STS may prove more valuable in differentiating the diverse sub‐types of mesenchymal neoplasms within this grouping. To this purpose we sought to characterize the mutation and expression profiles of canine STS. In this study we used whole exome capture (Agilent Sure Select Canine V2) to sequence 29 tumors, grade I‐III, from non‐visceral locations, and matched normal samples, along with RNAseq of tumor samples. For the WES data, 40‐170 million 150 bp paired‐end reads were obtained from Illumina sequencing which were mapped against CanFam3.1 genome via BWA and short variants were called and annotated Mutect2 and VEP tools, respectively. The median depth of sequencing for normals and tumors were 97X (range: 35X–128X) and 110X (range: 22X–133X), respectively. Additionally, RNAseq reads were sequenced from 29 tumors and mapped against CanFam3.1 genome via STAR and gene count data was generated by HTSeq‐count tool. The total number of somatic variants identified across 29 samples ranged from 275 to 4,196, of which, 6% to 31% were annotated as cDNA variants. The protein coding mutations per callable megabase ranged from 0.3 to 37.3. Known cancer genes (COSMIC database) with recurrent mutations were KMT2D(21% of the samples), TP53 (21%), CNTNAP2(14%) genes. Using the RNAseq data, we identified three samples carrying driver fusions of platelet derived growth factor B (PDGFB) and collagen genes. These gene fusions were confirmed through Sanger sequencing of amplified cDNA. To delineate the transcriptomic sub‐types, we used hierarchical and K‐means clustering methods. This resulted in 4 groups with similar expression profiles comprising of 11, 4, 8 and 6 samples in each. Further, genes set variation analysis (GSVA) was used to profile the distinct pathways across all 4 clusters. Preliminary data indicates that the 11‐sample and 6‐sample clusters had up‐regulated non‐homologous end joining pathway and immune response pathways, respectively. Further study of genes and pathways that are enriched in sample clusters will help in categorizing the canine STS tumors for diagnosis and treatment.

On the existence of young embedded clusters at high Galactic latitude

Careful analyses of photometric and star count data available for the nine putative young clusters identified by Camargo et al. (2015, 2016) at high Galactic latitudes reveal that none of the groups contain early-type stars, and most are not significant density enhancements above field level. 2MASS colours for stars in the groups match those of unreddened late-type dwarfs and giants, as expected for contamination by (mostly) thin disk objects. A simulation of one such field using only typical high latitude foreground stars yields a colour-magnitude diagram that is very similar to those constructed by Camargo et al. (2015, 2016) as evidence for their young groups as well as the means of deriving their reddenings and distances. Although some of the fields are coincident with clusters of galaxies, one must conclude that there is no evidence that the putative clusters are extremely young stellar groups.

The distribution function of the Galaxy's dark halo

Starting from the hypothesis that the Galaxy's dark halo responded adiabatically to the infall of baryons, we have constructed a self-consistent dynamical model of the Galaxy that satisfies a large number of observations, including measurements of gas terminal velocities and masers, the kinematics of 180 000 giant stars from the RAVE (RAdial Velocity Experiment) survey and star-count data from the Sloan Digital Sky Survey. The stellar disc and the dark halo are both specified by distribution functions of the action integrals. The model is obtained by extending the work of Piffl et al. from the construction of a single model to a systematic search of model space. Whereas the model of Piffl et al. violated constraints on the terminal-velocity curve, our model respects these constraints by adopting a long scalelength Rd = 3.66 kpc for the thin and thick discs. The model is, however, inconsistent with the measured optical depth for microlensing of bulge stars because it attributes too large a fraction of the density at R ≲ 3 kpc to dark matter rather than stars. Moreover, it now seems likely that the thick disc's scalelength is significantly shorter than the model implies. Shortening this scalelength would cause the constraints from the rotation curve to be violated anew. We conclude that we can now rule out adiabatic compression of our Galaxy's dark halo.

A NEW AUTO-GUIDING SYSTEM FOR CQUEAN

We develop a new auto-guiding system for the Camera for QUasars in the EArly uNiverse (CQUEAN). CQUEAN is an optical CCD camera system attached to the 2.1-m Otto-Struve Telescope (OST) at McDonald Observatory, USA. The new auto-guiding system differs from the original one in the following: instead of the cassegrain focus of the OST, it is attached to the finder scope; it has its own filter system for observation of bright targets; and it is controlled with the CQUEAN Auto-guiding Package, a newly developed auto-guiding program. Finder scope commands a very wide field of view at the expense of poorer light gathering power than that of the OST. Based on the star count data and the limiting magnitude of the system, we estimate there are more than 5.9 observable stars with a single FOV using the new auto-guiding CCD camera. An adapter is made to attach the system to the finder scope. The new auto-guiding system successfully guided the OST to obtain science data with CQUEAN during the test run in 2014 February. The FWHM and ellipticity distributions of stellar profiles on CQUEAN, images guided with the new auto-guiding system, indicate similar guiding capabilities with the original auto-guiding system but with slightly poorer guiding performance at longer exposures, as indicated by the position angle distribution. We conclude that the new auto-guiding system has overall similar guiding performance to the original system. The new auto-guiding system will be used for the second generation CQUEAN, but it can be used for other cassegrain instruments of the OST.

Preparing the Besançon Galaxy model for the comparison with Gaia data

From the Gaia mission, kinematic and star count data, together with the physical parameters of the stars - ages and metallicities-, will allow to characterise our Galaxy populations and, from that, the overall Galactic gravitational potential. One of the promising procedures to reach such goal will be to optimise the present Population Synthesis models by fitting, through robust statistical techniques, the large and small scale structure and kinematics parameters that best will reproduce Gaia data. As a first step we present here the comparison between the data from the Tycho-2 catalogue and the Besancon Galaxy Model simulations, as well as our present our work on the model optimization.

THE INNER GALACTIC BULGE: EVIDENCE FOR A NUCLEAR BAR?

Recent data from the VVV survey have strengthened evidence for a structural change in the Galactic bulge inwards of |l|<=4 deg. Here we show with an N-body barred galaxy simulation that a boxy bulge formed through the bar and buckling instabilities effortlessly matches measured bulge longitude profiles for red clump stars. The same simulation snapshot was earlier used to clarify the apparent boxy bulge - long bar dichotomy, for the same orientation and scaling. The change in the slope of the model longitude profiles in the inner few degrees is caused by a transition from highly elongated to more nearly axisymmetric isodensity contours in the inner boxy bulge. This transition is confined to a few degrees from the Galactic plane, thus the change of slope is predicted to disappear at higher Galactic latitudes. We also show that the nuclear star count map derived from this simulation snapshot displays a longitudinal asymmetry similar to that observed in the 2MASS data, but is less flattened to the Galactic plane than the 2MASS map. These results support the interpretation that the Galactic bulge originated from disk evolution, and question the evidence advanced from star count data for the existence of a secondary nuclear bar in the Milky Way.

Modeling the Newtonian dynamics for rotation curve analysis of thin-disk galaxies

We present an efficient, robust computational method for modeling the Newtonian dynamics for rotation curve analysis of thin-disk galaxies. With appropriate mathematical treatments, the apparent numerical difficulties associated with singularities in computing elliptic integrals are completely removed. Using a boundary element discretization procedure, the governing equations are transformed into a linear algebra matrix equation that can be solved by straightforward Gauss elimination in one step without further iterations. The numerical code implemented according to our algorithm can accurately determine the surface mass density distribution in a disk galaxy from a measured rotation curve (or vice versa). For a disk galaxy with a typical flat rotation curve, our modeling results show that the surface mass density monotonically decreases from the galactic center toward the periphery, according to Newtonian dynamics. In a large portion of the galaxy, the surface mass density follows an approximately exponential law of decay with respect to the galactic radial coordinate. Yet the radial scale length for the surface mass density seems to be generally larger than that of the measured brightness distribution, suggesting an increasing mass-to-light ratio with the radial distance in a disk galaxy. In a nondimensionalized form, our mathematical system contains a dimensionless parameter which we call the “galactic rotation number" that represents the gross ratio of centrifugal force and gravitational force. The value of this galactic rotation number is determined as part of the numerical solution. Through a systematic computational analysis, we have illustrated that the galactic rotation number remains within ±10% of 1.70 for a wide variety of rotation curves. This implies that the total mass in a disk galaxy is proportional to V02Rg, with V0 denoting the characteristic rotation velocity (such as the “flat" value in a typical rotation curve) and Rg the radius of the galactic disk. The predicted total galactic mass of the Milky Way is in good agreement with the star-count data.

INFORMATION ON THE MILKY WAY FROM THE TWO MICRON ALL SKY SURVEY WHOLE SKY STAR COUNT: THE STRUCTURE PARAMETERS

The Ks band differential star count of the Two Micron All Sky Survey (2MASS) is used to derive the global structure parameters of the smooth components of the Milky Way. To avoid complication introduced by other fine structures and significant extinction near and at the Galactic plane, we only consider Galactic latitude |b| > 30 degree data. The star count data is fitted with a threecomponent model: double exponential thin disk and thick disk, and a power law decay oblate halo. Using maximum likelihood the best-fit local density of thin disk is n0 = 0.030 +- 0.002 stars/pc^3. The best-fit scale-height and length of the thin disk are Hz1 = 360+-10 pc and Hr1 = 3.7+-1.0 kpc, and those of the thick disk are and Hz2 = 1020+-30 pc and Hr2 = 5.0+-1.0 kpc, the local thick-to-thin disk density ratio is f2 = 7+-1%. The best-fit axis ratio, power law index and local density ratio of the oblate halo are kappa = 0.55+-0.15, p = 2.6+-0.6 and fh = 0.20+-0:10%, respectively. Moreover, we find some degeneracy among the key parameters (e.g. n0,Hz1, f2 and Hz2). Any pair of these parameters are anticorrelated to each other. The 2MASS data can be well-fitted by several possible combinations of parameters. This is probably the reason that there is a wide range of values for the structure parameters in literature similar to this study. Since only medium and high Galactic latitude data are analyzed, the fitting is very insensitive to the scale-lengths of the disks.

Kinematics of Milky Way satellites in a Lambda cold dark matter universe

We investigate whether the subhalos of Lambda-CDM galaxy halos have potentials consistent with the observed properties of Milky Way satellites, particularly those with high-quality photometric and kinematic data: Fornax, Leo I, Sculptor, Sextans, and Carina. We compare spherical models with isotropic velocity dispersion tensors to the observed, circularly averaged star counts, line-of-sight velocity dispersion profiles and line-of-sight velocity distributions. We identify subhalos within the six high-resolution dark matter halos of the Aquarius Project for which the spherically averaged potentials result in excellent fits to each of the five galaxies. In particular, our simple one-integral models reproduce the observations in the inner regions, proving that these data are fully consistent with Lambda-CDM expectations and do not require cored dark matter distributions. For four of the five satellites the fits require moderately cusped {\it stellar} density profiles. The star count data for Leo I, however, do require a cored distribution of star counts. Current data suggest that these five satellites may be hosted by Lambda-CDM subhalos with maximum circular velocities in the range 10 to 30 km/s.

NEW LIMITS ON AN INTERMEDIATE-MASS BLACK HOLE IN OMEGA CENTAURI. II. DYNAMICAL MODELS

We present a detailed dynamical analysis of the projected density and kinematical data available for the globular cluster Omega Cen. We solve the spherical anisotropic Jeans equation to predict the projected profiles of the RMS velocity in each of the three orthogonal coordinate directions (line of sight, proper motion radial, and proper motion tangential). We fit the models to new HST star count and proper motion data near the cluster center presented in Paper I, combined with existing ground-based measurements. We also derive and model the Gauss-Hermite moments of the observed proper motion distributions. The projected density profile is consistent with being flat near the center, with an upper limit gamma=0.07 on the central logarithmic slope. The RMS proper motion profile is also consistent with being flat near the center, and there are no unusually fast-moving stars. The models provide a good fit and yield a 1-sigma upper limit MBH < 1.2E4 solar masses on the mass of a possible intermediate-mass black hole (IMBH). The inferred upper limit corresponds to MBH/Mtot < 0.43%. We combine this with results for other clusters and discuss the implications for globular cluster IMBH demographics. Tighter limits will be needed to rule out or establish whether globular clusters follow the same black hole demographics correlations as galaxies. The arguments put forward by Noyola et al. (2008) to suspect an IMBH in Omega Cen are not confirmed by our study; the IMBH mass they suggested is firmly ruled out.

Preparing the Besançon Galaxy Model for the comparison with Gaia data.

From the Gaia mission, kinematic and star count data, together with the physical parameters of the stars - ages and metallicities-, will allow to characterise our Galaxy populations and, from that, the overall Galactic gravitational potential. One of the promising procedures to reach such goal will be to optimise the present Population Synthesis models by fitting, through robust statistical techniques, the large and small scale structure and kinematics parameters that best will reproduce Gaia data. As a first step we present here the comparison between the data from the Tycho-2 catalogue and the Besancon Galaxy Model simulations, as well as our present and future work on the model optimization.

STRUCTURAL PARAMETERS OF SEVEN SMALL MAGELLANIC CLOUD INTERMEDIATE-AGE AND OLD STAR CLUSTERS

We present structural parameters for the seven intermediate-age and old star clusters NGC121, Lindsay 1, Kron 3, NGC339, NGC416, Lindsay 38, and NGC419 in the Small Magellanic Cloud. We fit King profiles and Elson, Fall, and Freeman profiles to both surface-brightness and star count data taken with the Advanced Camera for Surveys aboard the Hubble Space Telescope. Clusters older than 1 Gyr show a spread in cluster core radii that increases with age, while the youngest clusters have relatively compact cores. No evidence for post core collapse clusters was found. We find no correlation between core radius and distance from the SMC center, although consistent with other studies of dwarf galaxies, some relatively old and massive clusters have low densities. The oldest SMC star cluster, the only globular NGC121, is the most elliptical object of the studied clusters. No correlation is seen between ellipticity and distance from the SMC center. The structures of these massive intermediate-age (1-8 Gyr) SMC star clusters thus appear to primarily result from internal evolutionary processes.

KINEMATIC DISTANCES TO MOLECULAR CLOUDS IDENTIFIED IN THE GALACTIC RING SURVEY

Kinematic distances to 750 molecular clouds identified in the 13CO J = 1 → 0 Boston University–Five College Radio Astronomy Observatory Galactic Ring Survey (GRS) are derived assuming the Clemens rotation curve of the Galaxy. The kinematic distance ambiguity is resolved by examining the presence of H i self-absorption toward the 13CO emission peak of each cloud using the Very Large Array Galactic Plane Survey. We also identify 21 cm continuum sources embedded in the GRS clouds in order to use absorption features in the H i 21 cm continuum to distinguish between near and far kinematic distances. The Galactic distribution of GRS clouds is consistent with a four-arm model of the Milky Way. The locations of the Scutum-Crux and Perseus arms traced by GRS clouds match star-count data from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire star-count data. We conclude that molecular clouds must form in spiral arms and be short-lived (lifetimes < 107 yr) in order to explain the absence of massive, 13CO bright molecular clouds in the interarm space.

Are the Red Halos of Galaxies Made of Low‐Mass Stars? Constraints from Subdwarf Star Counts in the Milky Way Halo

Surface photometry detections of red and exceedingly faint halos around galaxies have resurrected the old question of whether some nonnegligible fraction of the missing baryons of the universe could be hiding in the form of faint, hydrogen-burning stars. The optical/near-infrared colors of these red halos have proved very difficult to reconcile with any normal type of stellar population, but can, in principle, be explained by advocating a bottom-heavy stellar initial mass function. This implies a high stellar mass-to-light ratio and hence a substantial baryonic mass locked up in such halos. Here we explore the constraints imposed by current observations of ordinary stellar halo subdwarfs on a putative red halo of low-mass stars around the Milky Way. Assuming structural parameters similar to those of the red halo recently detected in stacked images of external disk galaxies, we find that a smooth halo component with a bottom-heavy initial mass function is completely ruled out by current star count data for the Milky Way. All viable smooth red halo models with a density slope even remotely similar to that of the stacked halo moreover contain far too little mass to have any bearing on the missing-baryon problem. However, we note that these constraints can be sidestepped if the red halo stars are locked up in star clusters, and we discuss potential observations of other nearby galaxies that may be able to put such scenarios to the test.

3D outer bulge structure from near infrared star counts

We attempt to study the characteristics of the different stellar populations present in the Galactic central region. A Monte Carlo method is used to simultaneously fit 11 thin disc and triaxial outer bulge density parameters on (Ks, ) star count data in almost 100 windows from the DENIS near infrared large scale survey at -8° < l < 12° and b < 4°. Various bulge density profiles and luminosity functions were tested using a population synthesis scheme. The best models, selected by a maximum likelihood test, give the following description: the outer bulge is boxy, prolate, and oriented 10.6° ± 3° with respect to the Sun-center direction. It seems that the main bulge population is not older than 10 Gyr, but this preliminary result needs further work to be confirmed. A significant central hole is found in the middle of the thin disc. We discuss these results in regard to previous findings and the scenario of bulge formation.

Dark matter in dwarf spheroidals I. Models

This paper introduces a new two-parameter family of dwarf spheroidal (dSph) galaxy models. The mass distribution has a Plummer profile and falls like R−4 in projection, in agreement with the star-count data. The first free parameter controls the velocity anisotropy and the second controls the dark matter content. The dark matter distribution can be varied from one extreme of mass-follows-light through a near-isothermal halo with flat rotation curve to the other extreme of an extended dark halo with harmonic core. This family of models is explored analytically in some detail – the distribution functions, the intrinsic moments and the projected moments are all calculated. For the nearby Galactic dSphs, samples of hundreds of discrete radial velocities are becoming available. A technique is developed to extract the anisotropy and dark matter content from such data sets by maximizing the likelihood function of the sample of radial velocities. This is constructed from the distribution function and corrected for observational errors and the effects of binaries. Tests on simulated data sets show that samples of ∼1000 discrete radial velocities are ample to break the degeneracy between mass and anisotropy in the nearby dSphs. Interesting constraints can already be placed on the distribution of the dark matter with samples of ∼160 radial velocities (the size of the present-day data set for Draco). The Space Interferometry Mission or SIM allows very accurate differential astrometry at faint magnitudes. This can be used to measure the internal proper motions of stars in the nearby Galactic dSphs. Our simulations show that ∼100 proper motions are sufficient to demolish the mass–anisotropy degeneracy completely. The target stars in Draco are at magnitudes of V∼19–20 and the required proper motion accuracy is 3–6 μas yr-1. The measurement of the proper motions of a sample of ∼100 stars uncontaminated with binaries will take about 400 h of SIM time, or under 2 per cent of the mission lifetime.

Near-Infrared Photometric Variability of Stars toward the Orion A Molecular Cloud

We present an analysis of J, H, and K_s time-series photometry obtained with the southern 2MASS telescope over a 0.°84 × 6° region centered near the Trapezium region of the Orion Nebula cluster. These data are used to establish the near-infrared variability properties of pre–main-sequence stars in Orion on timescales of ~1–36 days, ~2 months, and ~2 years. A total of 1235 near-infrared variable stars are identified, ~93% of which are likely associated with the Orion A molecular cloud. The variable stars exhibit a diversity of photometric behavior with time, including cyclic fluctuations with periods up to 15 days, aperiodic day-to-day fluctuations, eclipses, slow drifts in brightness over 1 month or longer, colorless variability (within the noise limits of the data), stars that become redder as they fade, and stars that become bluer as they fade. The mean peak-to-peak amplitudes of the photometric fluctuations are ~0.2 mag in each band, and 77% of the variable stars have color variations less than 0.05 mag. The more extreme stars in our sample have amplitudes as large as ~2 mag and change in color by as much as ~1 mag. The typical timescale of the photometric fluctuations is less than a few days, indicating that near-infrared variability results primarily from short-term processes. We examine rotational modulation of cool and hot starspots, variable obscuration from an inner circumstellar disk, and changes in the mass accretion rate and other physical properties in a circumstellar disk as possible physical origins of the near-infrared variability. Cool spots alone can explain the observed variability characteristics in ~56%–77% of the stars, while the properties of the photometric fluctuations are more consistent with hot spots or extinction changes in at least 23% of the stars, and with variations in the disk mass accretion rate or inner disk radius in ~1% of our sample. However, differences between the details of the observations and the details of variability predicted by hot-spot, extinction, and accretion disk models suggest either that another variability mechanism not considered here may be operative or that the observed variability represents the net results of several of these phenomena. Analysis of the star-count data indicates that the Orion Nebula cluster is part of a larger area of enhanced stellar surface density that extends over a 0.°4 × 2.°4 (3.4 pc × 20 pc) region containing ~2700 stars brighter than Ks = 14 mag.

Stellar Population Studies with the SDSS. I. The Vertical Distribution of Stars in the Milky Way

We present star count data from the Sloan Digital Sky Survey for 5.8 × 105 stars brighter than g' = 21 mag over 279 deg2 in two samples north and south of the Galactic plane. Using these high-latitude (49° < |b| < 64°) star counts we determine the Sun's distance from the Galactic midplane to be 27 ± 4 pc and the scale height of the old thin disk to be 330 ± 3 pc. Because of the photometric accuracy and large area sky coverage of these data, the color-magnitude diagram clearly reveals a significant thick-disk population distinct in color from a Galactic halo population. The position of the thick-disk turnoff is at g'-r' ~ 0.33. Several questions about the existence of the thick disk and its origin are addressed through a set of model fits to the star count data. Our best-fit model gives a thick-disk scale height between 580 and 750 pc, below the original proposal of Gilmore and Reid, and the corresponding space number density normalization is 13%-6.5% of the thin disk. The conclusions reached in this paper favor a scenario in which the thick disk formed through the heating of a preexisting thin disk, with the heating mechanism being the merging of a satellite galaxy. The density law for the Galactic halo population is also investigated. We find that the data support a flattened halo with c/a ~ 0.55 ± 0.06 and a relatively flat power-law index (2.5 ± 0.3). The axis ratio of the visible halo found in this paper is compatible with that of dark halo, suggesting that they have the same shape and dynamical origin.

The new Basel high-latitude field star survey of the Galaxy

We discuss star count and three-color data for the two inner-Galaxy elds SA 107 and NGC 6171 observed in the new Basel RGU high-latitude eld star survey. Our analysis is based on the structural models of the Galactic population components that were derived from the previous studies of seven elds mainly in the outer Galaxy (Buser et al. 1998, 1999, hereafter Papers I and II, respectively). Apart from the canonical structural parameters, we here explore some of the special conditions prevailing in the transition region from high to low latitudes approaching the Galactic bulge, such as interstellar reddening, preponderant sampling of giants, and pos- sible large-scale radial metallicity gradients. We show that the data are consistent on a high condence level with a model incorporating an old-thin disk with local mean metallicityh(M=H)i = 0:13 0:21 dex at galactocentric distance R 7:3 kpc and radial abundance gradient @(M=H)=@x = 0:078 0:016 dex/kpc, and a thick disk with mean metallicityh(M=H)i = 0:730:15 dex and vertical metallicity gradient@(M=H)=@z = 0:070:03 dex/kpc. Any radial gradient of the thick disk is shown to be marginal, 0 @(M=H)=@x 0:02 dex/kpc. For the inner halo, we nd a gradient-less metal-weak component with mean metallicity h(M=H)i 1:8 0:3 dex but also evidence of a { possibly localized { metal-rich component havingh(M=H)i = 1:0 0:2 dex. These results provide an important further step toward a comprehensive and detailed mapping of the larger-scale density and metallicity structures of the Galaxy, to be derived from the full-survey data in 14 elds.

Star Counts and the Warped and Flaring Milky Way Disk

This paper reports the star count predictions of warped and flaring models of the outer Milky Way disk. These have been suggested as possible locations of the lenses responsible for the microlensing events towards the Large Magellanic Cloud (LMC). Three such models are investigated in detail and the theoretical predictions are confronted with {\it Hubble Space Telescope} (HST) star count data in 7 low latitude fields ($30^\circ < | b| < 40^\circ$). If the warped and flaring disk population has the same characteristics as disk stars in the solar neighbourhood, then the models can be unambiguously ruled out. Metallicity gradients are well-known in disk galaxies and may cause the outer disk population to differ in colors and luminosity from that locally. This effect is studied using a simple ansatz for the variation in the color-magnitude relation with position and while it is shown to lead to better agreement with the star counts, upper limits on the contribution of the warped and flaring disk to the optical depth are still below the value measured towards the LMC. Only if the warp is very asymmetric or if the luminosity function changes strongly with Galactocentric radius can the models be made consistent with the starcounts.